Re: [PATCH v3 04/10] drm/msm/A6xx: Implement preemption for A7XX targets
From: Connor Abbott
Date: Mon Sep 09 2024 - 08:22:52 EST
On Fri, Sep 6, 2024 at 9:03 PM Akhil P Oommen <quic_akhilpo@xxxxxxxxxxx> wrote:
>
> On Thu, Sep 05, 2024 at 04:51:22PM +0200, Antonino Maniscalco wrote:
> > This patch implements preemption feature for A6xx targets, this allows
> > the GPU to switch to a higher priority ringbuffer if one is ready. A6XX
> > hardware as such supports multiple levels of preemption granularities,
> > ranging from coarse grained(ringbuffer level) to a more fine grained
> > such as draw-call level or a bin boundary level preemption. This patch
> > enables the basic preemption level, with more fine grained preemption
> > support to follow.
> >
> > Signed-off-by: Sharat Masetty <smasetty@xxxxxxxxxxxxxx>
> > Signed-off-by: Antonino Maniscalco <antomani103@xxxxxxxxx>
> > Tested-by: Neil Armstrong <neil.armstrong@xxxxxxxxxx> # on SM8650-QRD
> > ---
> > drivers/gpu/drm/msm/Makefile | 1 +
> > drivers/gpu/drm/msm/adreno/a6xx_gpu.c | 293 +++++++++++++++++++++-
> > drivers/gpu/drm/msm/adreno/a6xx_gpu.h | 161 ++++++++++++
> > drivers/gpu/drm/msm/adreno/a6xx_preempt.c | 391 ++++++++++++++++++++++++++++++
> > drivers/gpu/drm/msm/msm_ringbuffer.h | 7 +
> > 5 files changed, 844 insertions(+), 9 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/msm/Makefile b/drivers/gpu/drm/msm/Makefile
> > index f5e2838c6a76..32e915109a59 100644
> > --- a/drivers/gpu/drm/msm/Makefile
> > +++ b/drivers/gpu/drm/msm/Makefile
> > @@ -23,6 +23,7 @@ adreno-y := \
> > adreno/a6xx_gpu.o \
> > adreno/a6xx_gmu.o \
> > adreno/a6xx_hfi.o \
> > + adreno/a6xx_preempt.o \
> >
> > adreno-$(CONFIG_DEBUG_FS) += adreno/a5xx_debugfs.o \
> >
> > diff --git a/drivers/gpu/drm/msm/adreno/a6xx_gpu.c b/drivers/gpu/drm/msm/adreno/a6xx_gpu.c
> > index 32a4faa93d7f..ed0b138a2d66 100644
> > --- a/drivers/gpu/drm/msm/adreno/a6xx_gpu.c
> > +++ b/drivers/gpu/drm/msm/adreno/a6xx_gpu.c
> > @@ -16,6 +16,83 @@
> >
> > #define GPU_PAS_ID 13
> >
> > +/* IFPC & Preemption static powerup restore list */
> > +static const uint32_t a7xx_pwrup_reglist[] = {
> > + REG_A6XX_UCHE_TRAP_BASE,
> > + REG_A6XX_UCHE_TRAP_BASE + 1,
> > + REG_A6XX_UCHE_WRITE_THRU_BASE,
> > + REG_A6XX_UCHE_WRITE_THRU_BASE + 1,
> > + REG_A6XX_UCHE_GMEM_RANGE_MIN,
> > + REG_A6XX_UCHE_GMEM_RANGE_MIN + 1,
> > + REG_A6XX_UCHE_GMEM_RANGE_MAX,
> > + REG_A6XX_UCHE_GMEM_RANGE_MAX + 1,
> > + REG_A6XX_UCHE_CACHE_WAYS,
> > + REG_A6XX_UCHE_MODE_CNTL,
> > + REG_A6XX_RB_NC_MODE_CNTL,
> > + REG_A6XX_RB_CMP_DBG_ECO_CNTL,
> > + REG_A7XX_GRAS_NC_MODE_CNTL,
> > + REG_A6XX_RB_CONTEXT_SWITCH_GMEM_SAVE_RESTORE,
> > + REG_A6XX_UCHE_GBIF_GX_CONFIG,
> > + REG_A6XX_UCHE_CLIENT_PF,
>
> REG_A6XX_TPL1_DBG_ECO_CNTL1 here. A friendly warning, missing a register
> in this list (and the below list) will lead to a very frustrating debug.
>
> > +};
> > +
> > +static const uint32_t a7xx_ifpc_pwrup_reglist[] = {
> > + REG_A6XX_TPL1_NC_MODE_CNTL,
> > + REG_A6XX_SP_NC_MODE_CNTL,
> > + REG_A6XX_CP_DBG_ECO_CNTL,
> > + REG_A6XX_CP_PROTECT_CNTL,
> > + REG_A6XX_CP_PROTECT(0),
> > + REG_A6XX_CP_PROTECT(1),
> > + REG_A6XX_CP_PROTECT(2),
> > + REG_A6XX_CP_PROTECT(3),
> > + REG_A6XX_CP_PROTECT(4),
> > + REG_A6XX_CP_PROTECT(5),
> > + REG_A6XX_CP_PROTECT(6),
> > + REG_A6XX_CP_PROTECT(7),
> > + REG_A6XX_CP_PROTECT(8),
> > + REG_A6XX_CP_PROTECT(9),
> > + REG_A6XX_CP_PROTECT(10),
> > + REG_A6XX_CP_PROTECT(11),
> > + REG_A6XX_CP_PROTECT(12),
> > + REG_A6XX_CP_PROTECT(13),
> > + REG_A6XX_CP_PROTECT(14),
> > + REG_A6XX_CP_PROTECT(15),
> > + REG_A6XX_CP_PROTECT(16),
> > + REG_A6XX_CP_PROTECT(17),
> > + REG_A6XX_CP_PROTECT(18),
> > + REG_A6XX_CP_PROTECT(19),
> > + REG_A6XX_CP_PROTECT(20),
> > + REG_A6XX_CP_PROTECT(21),
> > + REG_A6XX_CP_PROTECT(22),
> > + REG_A6XX_CP_PROTECT(23),
> > + REG_A6XX_CP_PROTECT(24),
> > + REG_A6XX_CP_PROTECT(25),
> > + REG_A6XX_CP_PROTECT(26),
> > + REG_A6XX_CP_PROTECT(27),
> > + REG_A6XX_CP_PROTECT(28),
> > + REG_A6XX_CP_PROTECT(29),
> > + REG_A6XX_CP_PROTECT(30),
> > + REG_A6XX_CP_PROTECT(31),
> > + REG_A6XX_CP_PROTECT(32),
> > + REG_A6XX_CP_PROTECT(33),
> > + REG_A6XX_CP_PROTECT(34),
> > + REG_A6XX_CP_PROTECT(35),
> > + REG_A6XX_CP_PROTECT(36),
> > + REG_A6XX_CP_PROTECT(37),
> > + REG_A6XX_CP_PROTECT(38),
> > + REG_A6XX_CP_PROTECT(39),
> > + REG_A6XX_CP_PROTECT(40),
> > + REG_A6XX_CP_PROTECT(41),
> > + REG_A6XX_CP_PROTECT(42),
> > + REG_A6XX_CP_PROTECT(43),
> > + REG_A6XX_CP_PROTECT(44),
> > + REG_A6XX_CP_PROTECT(45),
> > + REG_A6XX_CP_PROTECT(46),
> > + REG_A6XX_CP_PROTECT(47),
> > + REG_A6XX_CP_AHB_CNTL,
> > +};
> > +
> > +
> > static inline bool _a6xx_check_idle(struct msm_gpu *gpu)
> > {
> > struct adreno_gpu *adreno_gpu = to_adreno_gpu(gpu);
> > @@ -68,6 +145,8 @@ static void update_shadow_rptr(struct msm_gpu *gpu, struct msm_ringbuffer *ring)
> >
> > static void a6xx_flush(struct msm_gpu *gpu, struct msm_ringbuffer *ring)
> > {
> > + struct adreno_gpu *adreno_gpu = to_adreno_gpu(gpu);
> > + struct a6xx_gpu *a6xx_gpu = to_a6xx_gpu(adreno_gpu);
> > uint32_t wptr;
> > unsigned long flags;
> >
> > @@ -81,12 +160,26 @@ static void a6xx_flush(struct msm_gpu *gpu, struct msm_ringbuffer *ring)
> > /* Make sure to wrap wptr if we need to */
> > wptr = get_wptr(ring);
> >
> > - spin_unlock_irqrestore(&ring->preempt_lock, flags);
> > -
> > /* Make sure everything is posted before making a decision */
> > mb();
>
> This looks unnecessary.
>
> >
> > - gpu_write(gpu, REG_A6XX_CP_RB_WPTR, wptr);
> > + /* Update HW if this is the current ring and we are not in preempt*/
> > + if (!a6xx_in_preempt(a6xx_gpu)) {
> > + /*
> > + * Order the reads of the preempt state and cur_ring. This
> > + * matches the barrier after writing cur_ring.
> > + */
> > + rmb();
>
> we can use the lighter smp variant here.
>
> > +
> > + if (a6xx_gpu->cur_ring == ring)
> > + gpu_write(gpu, REG_A6XX_CP_RB_WPTR, wptr);
> > + else
> > + ring->skip_inline_wptr = true;
> > + } else {
> > + ring->skip_inline_wptr = true;
> > + }
> > +
> > + spin_unlock_irqrestore(&ring->preempt_lock, flags);
> > }
> >
> > static void get_stats_counter(struct msm_ringbuffer *ring, u32 counter,
> > @@ -138,12 +231,14 @@ static void a6xx_set_pagetable(struct a6xx_gpu *a6xx_gpu,
>
> set_pagetable checks "cur_ctx_seqno" to see if pt switch is needed or
> not. This is currently not tracked separately for each ring. Can you
> please check that?
>
> I wonder why that didn't cause any gpu errors in testing. Not sure if I
> am missing something.
>
> >
> > /*
> > * Write the new TTBR0 to the memstore. This is good for debugging.
> > + * Needed for preemption
> > */
> > - OUT_PKT7(ring, CP_MEM_WRITE, 4);
> > + OUT_PKT7(ring, CP_MEM_WRITE, 5);
> > OUT_RING(ring, CP_MEM_WRITE_0_ADDR_LO(lower_32_bits(memptr)));
> > OUT_RING(ring, CP_MEM_WRITE_1_ADDR_HI(upper_32_bits(memptr)));
> > OUT_RING(ring, lower_32_bits(ttbr));
> > - OUT_RING(ring, (asid << 16) | upper_32_bits(ttbr));
> > + OUT_RING(ring, upper_32_bits(ttbr));
> > + OUT_RING(ring, ctx->seqno);
> >
> > /*
> > * Sync both threads after switching pagetables and enable BR only
> > @@ -268,6 +363,43 @@ static void a6xx_submit(struct msm_gpu *gpu, struct msm_gem_submit *submit)
> > a6xx_flush(gpu, ring);
> > }
> >
> > +static void a6xx_emit_set_pseudo_reg(struct msm_ringbuffer *ring,
> > + struct a6xx_gpu *a6xx_gpu, struct msm_gpu_submitqueue *queue)
> > +{
> > + u64 preempt_offset_priv_secure;
> > +
> > + OUT_PKT7(ring, CP_SET_PSEUDO_REG, 15);
> > +
> > + OUT_RING(ring, SMMU_INFO);
> > + /* don't save SMMU, we write the record from the kernel instead */
> > + OUT_RING(ring, 0);
> > + OUT_RING(ring, 0);
> > +
> > + /* privileged and non secure buffer save */
> > + OUT_RING(ring, NON_SECURE_SAVE_ADDR);
> > + OUT_RING(ring, lower_32_bits(
> > + a6xx_gpu->preempt_iova[ring->id] + PREEMPT_OFFSET_PRIV_NON_SECURE));
> > + OUT_RING(ring, upper_32_bits(
> > + a6xx_gpu->preempt_iova[ring->id] + PREEMPT_OFFSET_PRIV_NON_SECURE));
> > + OUT_RING(ring, SECURE_SAVE_ADDR);
> > + preempt_offset_priv_secure =
> > + PREEMPT_OFFSET_PRIV_SECURE(a6xx_gpu->base.info->preempt_record_size);
> > + OUT_RING(ring, lower_32_bits(
> > + a6xx_gpu->preempt_iova[ring->id] + preempt_offset_priv_secure));
> > + OUT_RING(ring, upper_32_bits(
> > + a6xx_gpu->preempt_iova[ring->id] + preempt_offset_priv_secure));
> > +
> > + /* user context buffer save, seems to be unnused by fw */
> > + OUT_RING(ring, NON_PRIV_SAVE_ADDR);
> > + OUT_RING(ring, 0);
> > + OUT_RING(ring, 0);
> > +
> > + OUT_RING(ring, COUNTER);
> > + /* seems OK to set to 0 to disable it */
> > + OUT_RING(ring, 0);
> > + OUT_RING(ring, 0);
> > +}
> > +
> > static void a7xx_submit(struct msm_gpu *gpu, struct msm_gem_submit *submit)
> > {
> > unsigned int index = submit->seqno % MSM_GPU_SUBMIT_STATS_COUNT;
> > @@ -283,6 +415,13 @@ static void a7xx_submit(struct msm_gpu *gpu, struct msm_gem_submit *submit)
> > OUT_PKT7(ring, CP_THREAD_CONTROL, 1);
> > OUT_RING(ring, CP_THREAD_CONTROL_0_SYNC_THREADS | CP_SET_THREAD_BR);
> >
> > + /*
> > + * If preemption is enabled, then set the pseudo register for the save
> > + * sequence
> > + */
> > + if (gpu->nr_rings > 1)
> > + a6xx_emit_set_pseudo_reg(ring, a6xx_gpu, submit->queue);
>
> Can we move this after set_pagetable()?
>
> > +
> > a6xx_set_pagetable(a6xx_gpu, ring, submit->queue->ctx);
> >
> > get_stats_counter(ring, REG_A7XX_RBBM_PERFCTR_CP(0),
> > @@ -376,6 +515,8 @@ static void a7xx_submit(struct msm_gpu *gpu, struct msm_gem_submit *submit)
> > OUT_RING(ring, upper_32_bits(rbmemptr(ring, bv_fence)));
> > OUT_RING(ring, submit->seqno);
> >
> > + a6xx_gpu->last_seqno[ring->id] = submit->seqno;
> > +
> > /* write the ringbuffer timestamp */
> > OUT_PKT7(ring, CP_EVENT_WRITE, 4);
> > OUT_RING(ring, CACHE_CLEAN | CP_EVENT_WRITE_0_IRQ | BIT(27));
> > @@ -389,10 +530,32 @@ static void a7xx_submit(struct msm_gpu *gpu, struct msm_gem_submit *submit)
> > OUT_PKT7(ring, CP_SET_MARKER, 1);
> > OUT_RING(ring, 0x100); /* IFPC enable */
> >
> > + /* If preemption is enabled */
> > + if (gpu->nr_rings > 1) {
> > + /* Yield the floor on command completion */
> > + OUT_PKT7(ring, CP_CONTEXT_SWITCH_YIELD, 4);
> > +
> > + /*
> > + * If dword[2:1] are non zero, they specify an address for
> > + * the CP to write the value of dword[3] to on preemption
> > + * complete. Write 0 to skip the write
> > + */
> > + OUT_RING(ring, 0x00);
> > + OUT_RING(ring, 0x00);
> > + /* Data value - not used if the address above is 0 */
> > + OUT_RING(ring, 0x01);
> > + /* generate interrupt on preemption completion */
> > + OUT_RING(ring, 0x00);
> > + }
> > +
> > +
> > trace_msm_gpu_submit_flush(submit,
> > gpu_read64(gpu, REG_A6XX_CP_ALWAYS_ON_COUNTER));
> >
> > a6xx_flush(gpu, ring);
> > +
> > + /* Check to see if we need to start preemption */
> > + a6xx_preempt_trigger(gpu);
> > }
> >
> > static void a6xx_set_hwcg(struct msm_gpu *gpu, bool state)
> > @@ -588,6 +751,89 @@ static void a6xx_set_ubwc_config(struct msm_gpu *gpu)
> > adreno_gpu->ubwc_config.min_acc_len << 23 | hbb_lo << 21);
> > }
> >
> > +static void a7xx_patch_pwrup_reglist(struct msm_gpu *gpu)
> > +{
> > + struct adreno_gpu *adreno_gpu = to_adreno_gpu(gpu);
> > + struct a6xx_gpu *a6xx_gpu = to_a6xx_gpu(adreno_gpu);
> > + struct adreno_reglist_list reglist[2];
> > + void *ptr = a6xx_gpu->pwrup_reglist_ptr;
> > + struct cpu_gpu_lock *lock = ptr;
> > + u32 *dest = (u32 *)&lock->regs[0];
> > + int i, j;
> > +
> This sequence is required only once. We can use a flag to check and bail out
> next time.
>
> > + lock->gpu_req = lock->cpu_req = lock->turn = 0;
> > + lock->ifpc_list_len = ARRAY_SIZE(a7xx_ifpc_pwrup_reglist);
> > + lock->preemption_list_len = ARRAY_SIZE(a7xx_pwrup_reglist);
> > +
> > + /* Static IFPC-only registers */
> > + reglist[0].regs = a7xx_ifpc_pwrup_reglist;
> > + reglist[0].count = ARRAY_SIZE(a7xx_ifpc_pwrup_reglist);
> > + lock->ifpc_list_len = reglist[0].count;
> > +
> > + /* Static IFPC + preemption registers */
> > + reglist[1].regs = a7xx_pwrup_reglist;
> > + reglist[1].count = ARRAY_SIZE(a7xx_pwrup_reglist);
> > + lock->preemption_list_len = reglist[1].count;
> > +
> > + /*
> > + * For each entry in each of the lists, write the offset and the current
> > + * register value into the GPU buffer
> > + */
> > + for (i = 0; i < 2; i++) {
> > + const u32 *r = reglist[i].regs;
> > +
> > + for (j = 0; j < reglist[i].count; j++) {
> > + *dest++ = r[j];
> > + *dest++ = gpu_read(gpu, r[j]);
> > + }
> > + }
> > +
> > + /*
> > + * The overall register list is composed of
> > + * 1. Static IFPC-only registers
> > + * 2. Static IFPC + preemption registers
> > + * 3. Dynamic IFPC + preemption registers (ex: perfcounter selects)
> > + *
> > + * The first two lists are static. Size of these lists are stored as
> > + * number of pairs in ifpc_list_len and preemption_list_len
> > + * respectively. With concurrent binning, Some of the perfcounter
> > + * registers being virtualized, CP needs to know the pipe id to program
> > + * the aperture inorder to restore the same. Thus, third list is a
> > + * dynamic list with triplets as
> > + * (<aperture, shifted 12 bits> <address> <data>), and the length is
> > + * stored as number for triplets in dynamic_list_len.
> > + */
> > + lock->dynamic_list_len = 0;
> > +}
> > +
> > +static int a7xx_preempt_start(struct msm_gpu *gpu)
> > +{
> > + struct adreno_gpu *adreno_gpu = to_adreno_gpu(gpu);
> > + struct a6xx_gpu *a6xx_gpu = to_a6xx_gpu(adreno_gpu);
> > + struct msm_ringbuffer *ring = gpu->rb[0];
> > +
> > + if (gpu->nr_rings <= 1)
> > + return 0;
> > +
> > + /* Turn CP protection off */
> > + OUT_PKT7(ring, CP_SET_PROTECTED_MODE, 1);
> > + OUT_RING(ring, 0);
> > +
> > + a6xx_emit_set_pseudo_reg(ring, a6xx_gpu, NULL);
> > +
> > + /* Yield the floor on command completion */
> > + OUT_PKT7(ring, CP_CONTEXT_SWITCH_YIELD, 4);
> > + OUT_RING(ring, 0x00);
> > + OUT_RING(ring, 0x00);
> > + OUT_RING(ring, 0x01);
>
> Looks like kgsl use 0x00 here. Not sure if that matters!
>
> > + /* Generate interrupt on preemption completion */
> > + OUT_RING(ring, 0x00);
> > +
> > + a6xx_flush(gpu, ring);
> > +
> > + return a6xx_idle(gpu, ring) ? 0 : -EINVAL;
> > +}
> > +
> > static int a6xx_cp_init(struct msm_gpu *gpu)
> > {
> > struct msm_ringbuffer *ring = gpu->rb[0];
> > @@ -619,6 +865,8 @@ static int a6xx_cp_init(struct msm_gpu *gpu)
> >
> > static int a7xx_cp_init(struct msm_gpu *gpu)
> > {
> > + struct adreno_gpu *adreno_gpu = to_adreno_gpu(gpu);
> > + struct a6xx_gpu *a6xx_gpu = to_a6xx_gpu(adreno_gpu);
> > struct msm_ringbuffer *ring = gpu->rb[0];
> > u32 mask;
> >
> > @@ -626,6 +874,8 @@ static int a7xx_cp_init(struct msm_gpu *gpu)
> > OUT_PKT7(ring, CP_THREAD_CONTROL, 1);
> > OUT_RING(ring, BIT(27));
> >
> > + a7xx_patch_pwrup_reglist(gpu);
> > +
>
> Looks out of place. I guess you kept it here to avoid an extra a7x
> check. At least we should move this before the above pm4 packets.
>
> > OUT_PKT7(ring, CP_ME_INIT, 7);
> >
> > /* Use multiple HW contexts */
> > @@ -656,11 +906,11 @@ static int a7xx_cp_init(struct msm_gpu *gpu)
> >
> > /* *Don't* send a power up reg list for concurrent binning (TODO) */
> > /* Lo address */
> > - OUT_RING(ring, 0x00000000);
> > + OUT_RING(ring, lower_32_bits(a6xx_gpu->pwrup_reglist_iova));
> > /* Hi address */
> > - OUT_RING(ring, 0x00000000);
> > + OUT_RING(ring, upper_32_bits(a6xx_gpu->pwrup_reglist_iova));
> > /* BIT(31) set => read the regs from the list */
> > - OUT_RING(ring, 0x00000000);
> > + OUT_RING(ring, BIT(31));
> >
> > a6xx_flush(gpu, ring);
> > return a6xx_idle(gpu, ring) ? 0 : -EINVAL;
> > @@ -784,6 +1034,16 @@ static int a6xx_ucode_load(struct msm_gpu *gpu)
> > msm_gem_object_set_name(a6xx_gpu->shadow_bo, "shadow");
> > }
> >
> > + a6xx_gpu->pwrup_reglist_ptr = msm_gem_kernel_new(gpu->dev, PAGE_SIZE,
> > + MSM_BO_WC | MSM_BO_MAP_PRIV,
> > + gpu->aspace, &a6xx_gpu->pwrup_reglist_bo,
> > + &a6xx_gpu->pwrup_reglist_iova);
> > +
> > + if (IS_ERR(a6xx_gpu->pwrup_reglist_ptr))
> > + return PTR_ERR(a6xx_gpu->pwrup_reglist_ptr);
> > +
> > + msm_gem_object_set_name(a6xx_gpu->pwrup_reglist_bo, "pwrup_reglist");
> > +
> > return 0;
> > }
> >
> > @@ -1127,6 +1387,8 @@ static int hw_init(struct msm_gpu *gpu)
> > if (a6xx_gpu->shadow_bo) {
> > gpu_write64(gpu, REG_A6XX_CP_RB_RPTR_ADDR,
> > shadowptr(a6xx_gpu, gpu->rb[0]));
> > + for (unsigned int i = 0; i < gpu->nr_rings; i++)
> > + a6xx_gpu->shadow[i] = 0;
> > }
> >
> > /* ..which means "always" on A7xx, also for BV shadow */
> > @@ -1135,6 +1397,8 @@ static int hw_init(struct msm_gpu *gpu)
> > rbmemptr(gpu->rb[0], bv_rptr));
> > }
> >
> > + a6xx_preempt_hw_init(gpu);
> > +
> > /* Always come up on rb 0 */
> > a6xx_gpu->cur_ring = gpu->rb[0];
> >
> > @@ -1180,6 +1444,10 @@ static int hw_init(struct msm_gpu *gpu)
> > out:
> > if (adreno_has_gmu_wrapper(adreno_gpu))
> > return ret;
> > +
> > + /* Last step - yield the ringbuffer */
> > + a7xx_preempt_start(gpu);
> > +
> > /*
> > * Tell the GMU that we are done touching the GPU and it can start power
> > * management
> > @@ -1557,8 +1825,13 @@ static irqreturn_t a6xx_irq(struct msm_gpu *gpu)
> > if (status & A6XX_RBBM_INT_0_MASK_SWFUSEVIOLATION)
> > a7xx_sw_fuse_violation_irq(gpu);
> >
> > - if (status & A6XX_RBBM_INT_0_MASK_CP_CACHE_FLUSH_TS)
> > + if (status & A6XX_RBBM_INT_0_MASK_CP_CACHE_FLUSH_TS) {
> > msm_gpu_retire(gpu);
> > + a6xx_preempt_trigger(gpu);
> > + }
> > +
> > + if (status & A6XX_RBBM_INT_0_MASK_CP_SW)
> > + a6xx_preempt_irq(gpu);
> >
> > return IRQ_HANDLED;
> > }
> > @@ -2331,6 +2604,8 @@ struct msm_gpu *a6xx_gpu_init(struct drm_device *dev)
> > a6xx_fault_handler);
> >
> > a6xx_calc_ubwc_config(adreno_gpu);
> > + /* Set up the preemption specific bits and pieces for each ringbuffer */
> > + a6xx_preempt_init(gpu);
> >
> > return gpu;
> > }
> > diff --git a/drivers/gpu/drm/msm/adreno/a6xx_gpu.h b/drivers/gpu/drm/msm/adreno/a6xx_gpu.h
> > index e3e5c53ae8af..da10060e38dc 100644
> > --- a/drivers/gpu/drm/msm/adreno/a6xx_gpu.h
> > +++ b/drivers/gpu/drm/msm/adreno/a6xx_gpu.h
> > @@ -12,6 +12,31 @@
> >
> > extern bool hang_debug;
> >
> > +struct cpu_gpu_lock {
> > + uint32_t gpu_req;
> > + uint32_t cpu_req;
> > + uint32_t turn;
> > + union {
> > + struct {
> > + uint16_t list_length;
> > + uint16_t list_offset;
> > + };
> > + struct {
> > + uint8_t ifpc_list_len;
> > + uint8_t preemption_list_len;
> > + uint16_t dynamic_list_len;
> > + };
> > + };
> > + uint64_t regs[62];
> > +};
> > +
> > +struct adreno_reglist_list {
> > + /** @reg: List of register **/
> > + const u32 *regs;
> > + /** @count: Number of registers in the list **/
> > + u32 count;
> > +};
> > +
> > /**
> > * struct a6xx_info - a6xx specific information from device table
> > *
> > @@ -31,6 +56,20 @@ struct a6xx_gpu {
> > uint64_t sqe_iova;
> >
> > struct msm_ringbuffer *cur_ring;
> > + struct msm_ringbuffer *next_ring;
> > +
> > + struct drm_gem_object *preempt_bo[MSM_GPU_MAX_RINGS];
> > + void *preempt[MSM_GPU_MAX_RINGS];
> > + uint64_t preempt_iova[MSM_GPU_MAX_RINGS];
> > + uint32_t last_seqno[MSM_GPU_MAX_RINGS];
> > +
> > + atomic_t preempt_state;
> > + spinlock_t eval_lock;
> > + struct timer_list preempt_timer;
> > +
> > + unsigned int preempt_level;
> > + bool uses_gmem;
> > + bool skip_save_restore;
> >
> > struct a6xx_gmu gmu;
> >
> > @@ -38,6 +77,10 @@ struct a6xx_gpu {
> > uint64_t shadow_iova;
> > uint32_t *shadow;
> >
> > + struct drm_gem_object *pwrup_reglist_bo;
> > + void *pwrup_reglist_ptr;
> > + uint64_t pwrup_reglist_iova;
> > +
> > bool has_whereami;
> >
> > void __iomem *llc_mmio;
> > @@ -49,6 +92,105 @@ struct a6xx_gpu {
> >
> > #define to_a6xx_gpu(x) container_of(x, struct a6xx_gpu, base)
> >
> > +/*
> > + * In order to do lockless preemption we use a simple state machine to progress
> > + * through the process.
> > + *
> > + * PREEMPT_NONE - no preemption in progress. Next state START.
> > + * PREEMPT_START - The trigger is evaluating if preemption is possible. Next
> > + * states: TRIGGERED, NONE
> > + * PREEMPT_FINISH - An intermediate state before moving back to NONE. Next
> > + * state: NONE.
> > + * PREEMPT_TRIGGERED: A preemption has been executed on the hardware. Next
> > + * states: FAULTED, PENDING
> > + * PREEMPT_FAULTED: A preemption timed out (never completed). This will trigger
> > + * recovery. Next state: N/A
> > + * PREEMPT_PENDING: Preemption complete interrupt fired - the callback is
> > + * checking the success of the operation. Next state: FAULTED, NONE.
> > + */
> > +
> > +enum a6xx_preempt_state {
> > + PREEMPT_NONE = 0,
> > + PREEMPT_START,
> > + PREEMPT_FINISH,
> > + PREEMPT_TRIGGERED,
> > + PREEMPT_FAULTED,
> > + PREEMPT_PENDING,
> > +};
> > +
> > +/*
> > + * struct a6xx_preempt_record is a shared buffer between the microcode and the
> > + * CPU to store the state for preemption. The record itself is much larger
> > + * (2112k) but most of that is used by the CP for storage.
> > + *
> > + * There is a preemption record assigned per ringbuffer. When the CPU triggers a
> > + * preemption, it fills out the record with the useful information (wptr, ring
> > + * base, etc) and the microcode uses that information to set up the CP following
> > + * the preemption. When a ring is switched out, the CP will save the ringbuffer
> > + * state back to the record. In this way, once the records are properly set up
> > + * the CPU can quickly switch back and forth between ringbuffers by only
> > + * updating a few registers (often only the wptr).
> > + *
> > + * These are the CPU aware registers in the record:
> > + * @magic: Must always be 0xAE399D6EUL
> > + * @info: Type of the record - written 0 by the CPU, updated by the CP
> > + * @errno: preemption error record
> > + * @data: Data field in YIELD and SET_MARKER packets, Written and used by CP
> > + * @cntl: Value of RB_CNTL written by CPU, save/restored by CP
> > + * @rptr: Value of RB_RPTR written by CPU, save/restored by CP
> > + * @wptr: Value of RB_WPTR written by CPU, save/restored by CP
> > + * @_pad: Reserved/padding
> > + * @rptr_addr: Value of RB_RPTR_ADDR_LO|HI written by CPU, save/restored by CP
> > + * @rbase: Value of RB_BASE written by CPU, save/restored by CP
> > + * @counter: GPU address of the storage area for the preemption counters
>
> doc missing for bv_rptr_addr.
>
> > + */
> > +struct a6xx_preempt_record {
> > + u32 magic;
> > + u32 info;
> > + u32 errno;
> > + u32 data;
> > + u32 cntl;
> > + u32 rptr;
> > + u32 wptr;
> > + u32 _pad;
> > + u64 rptr_addr;
> > + u64 rbase;
> > + u64 counter;
> > + u64 bv_rptr_addr;
> > +};
> > +
> > +#define A6XX_PREEMPT_RECORD_MAGIC 0xAE399D6EUL
> > +
> > +#define PREEMPT_RECORD_SIZE_FALLBACK(size) \
> > + ((size) == 0 ? 4192 * SZ_1K : (size))
> > +
> > +#define PREEMPT_OFFSET_SMMU_INFO 0
> > +#define PREEMPT_OFFSET_PRIV_NON_SECURE (PREEMPT_OFFSET_SMMU_INFO + 4096)
> > +#define PREEMPT_OFFSET_PRIV_SECURE(size) \
> > + (PREEMPT_OFFSET_PRIV_NON_SECURE + PREEMPT_RECORD_SIZE_FALLBACK(size))
> > +#define PREEMPT_SIZE(size) \
> > + (PREEMPT_OFFSET_PRIV_SECURE(size) + PREEMPT_RECORD_SIZE_FALLBACK(size))
> > +
> > +/*
> > + * The preemption counter block is a storage area for the value of the
> > + * preemption counters that are saved immediately before context switch. We
> > + * append it on to the end of the allocation for the preemption record.
> > + */
> > +#define A6XX_PREEMPT_COUNTER_SIZE (16 * 4)
> > +
> > +#define A6XX_PREEMPT_USER_RECORD_SIZE (192 * 1024)
>
> Unused.
>
> > +
> > +struct a7xx_cp_smmu_info {
> > + u32 magic;
> > + u32 _pad4;
> > + u64 ttbr0;
> > + u32 asid;
> > + u32 context_idr;
> > + u32 context_bank;
> > +};
> > +
> > +#define GEN7_CP_SMMU_INFO_MAGIC 0x241350d5UL
> > +
> > /*
> > * Given a register and a count, return a value to program into
> > * REG_CP_PROTECT_REG(n) - this will block both reads and writes for
> > @@ -106,6 +248,25 @@ int a6xx_gmu_init(struct a6xx_gpu *a6xx_gpu, struct device_node *node);
> > int a6xx_gmu_wrapper_init(struct a6xx_gpu *a6xx_gpu, struct device_node *node);
> > void a6xx_gmu_remove(struct a6xx_gpu *a6xx_gpu);
> >
> > +void a6xx_preempt_init(struct msm_gpu *gpu);
> > +void a6xx_preempt_hw_init(struct msm_gpu *gpu);
> > +void a6xx_preempt_trigger(struct msm_gpu *gpu);
> > +void a6xx_preempt_irq(struct msm_gpu *gpu);
> > +void a6xx_preempt_fini(struct msm_gpu *gpu);
> > +int a6xx_preempt_submitqueue_setup(struct msm_gpu *gpu,
> > + struct msm_gpu_submitqueue *queue);
> > +void a6xx_preempt_submitqueue_close(struct msm_gpu *gpu,
> > + struct msm_gpu_submitqueue *queue);
> > +
> > +/* Return true if we are in a preempt state */
> > +static inline bool a6xx_in_preempt(struct a6xx_gpu *a6xx_gpu)
> > +{
> > + int preempt_state = atomic_read(&a6xx_gpu->preempt_state);
>
> I think we should keep a matching barrier before the 'read' similar to the one used in the
> set_preempt_state helper.
Good idea, but for the one case we found where it matters (the
a6xx_flush() vs. updating the ring in a6xx_preempt_irq() race) the
barrier needs to be after the read. The sequence is something like:
Thread A:
a6xx_gpu->cur_ring = a6xx_gpu->next_ring;
a6xx_gpu->preempt_state = PREEMPT_FINISH;
Thread B:
read a6xx_gpu->preempt_state;
read a6xx_gpu->cur_ring;
And if the read to preempt_state returns PREEMPT_FINISH, then we need
cur_ring to reflect the ring we switched to. (I discovered this the
hard way from debugging deadlocks...)
So, maybe add a smp_rmb() before and after, then drop the explicit
barrier in a6xx_flush()?
>
> > +
> > + return !(preempt_state == PREEMPT_NONE ||
> > + preempt_state == PREEMPT_FINISH);
> > +}
> > +
> > void a6xx_gmu_set_freq(struct msm_gpu *gpu, struct dev_pm_opp *opp,
> > bool suspended);
> > unsigned long a6xx_gmu_get_freq(struct msm_gpu *gpu);
> > diff --git a/drivers/gpu/drm/msm/adreno/a6xx_preempt.c b/drivers/gpu/drm/msm/adreno/a6xx_preempt.c
> > new file mode 100644
> > index 000000000000..1caff76aca6e
> > --- /dev/null
> > +++ b/drivers/gpu/drm/msm/adreno/a6xx_preempt.c
> > @@ -0,0 +1,391 @@
> > +// SPDX-License-Identifier: GPL-2.0
> > +/* Copyright (c) 2018, The Linux Foundation. All rights reserved. */
> > +/* Copyright (c) 2023 Collabora, Ltd. */
> > +/* Copyright (c) 2024 Valve Corporation */
> > +
> > +#include "msm_gem.h"
> > +#include "a6xx_gpu.h"
> > +#include "a6xx_gmu.xml.h"
> > +#include "msm_mmu.h"
> > +
> > +/*
> > + * Try to transition the preemption state from old to new. Return
> > + * true on success or false if the original state wasn't 'old'
> > + */
> > +static inline bool try_preempt_state(struct a6xx_gpu *a6xx_gpu,
> > + enum a6xx_preempt_state old, enum a6xx_preempt_state new)
> > +{
> > + enum a6xx_preempt_state cur = atomic_cmpxchg(&a6xx_gpu->preempt_state,
> > + old, new);
> > +
> > + return (cur == old);
> > +}
> > +
> > +/*
> > + * Force the preemption state to the specified state. This is used in cases
> > + * where the current state is known and won't change
> > + */
> > +static inline void set_preempt_state(struct a6xx_gpu *gpu,
> > + enum a6xx_preempt_state new)
> > +{
> > + /*
> > + * preempt_state may be read by other cores trying to trigger a
> > + * preemption or in the interrupt handler so barriers are needed
> > + * before...
> > + */
> > + smp_mb__before_atomic();
> > + atomic_set(&gpu->preempt_state, new);
> > + /* ... and after*/
> > + smp_mb__after_atomic();
> > +}
> > +
> > +/* Write the most recent wptr for the given ring into the hardware */
> > +static inline void update_wptr(struct msm_gpu *gpu, struct msm_ringbuffer *ring)
> > +{
> > + unsigned long flags;
> > + uint32_t wptr;
> > +
> > + if (!ring)
>
> Is this ever true?
>
> > + return;
> > +
> > + spin_lock_irqsave(&ring->preempt_lock, flags);
> > +
> > + if (ring->skip_inline_wptr) {
> > + wptr = get_wptr(ring);
> > +
> > + gpu_write(gpu, REG_A6XX_CP_RB_WPTR, wptr);
> > +
> > + ring->skip_inline_wptr = false;
> > + }
> > +
> > + spin_unlock_irqrestore(&ring->preempt_lock, flags);
> > +}
> > +
> > +/* Return the highest priority ringbuffer with something in it */
> > +static struct msm_ringbuffer *get_next_ring(struct msm_gpu *gpu)
> > +{
> > + struct adreno_gpu *adreno_gpu = to_adreno_gpu(gpu);
> > + struct a6xx_gpu *a6xx_gpu = to_a6xx_gpu(adreno_gpu);
> > +
> > + unsigned long flags;
> > + int i;
> > +
> > + for (i = 0; i < gpu->nr_rings; i++) {
> > + bool empty;
> > + struct msm_ringbuffer *ring = gpu->rb[i];
> > +
> > + spin_lock_irqsave(&ring->preempt_lock, flags);
> > + empty = (get_wptr(ring) == gpu->funcs->get_rptr(gpu, ring));
> > + if (!empty && ring == a6xx_gpu->cur_ring)
> > + empty = ring->memptrs->fence == a6xx_gpu->last_seqno[i];
> > + spin_unlock_irqrestore(&ring->preempt_lock, flags);
> > +
> > + if (!empty)
> > + return ring;
> > + }
> > +
> > + return NULL;
> > +}
> > +
> > +static void a6xx_preempt_timer(struct timer_list *t)
> > +{
> > + struct a6xx_gpu *a6xx_gpu = from_timer(a6xx_gpu, t, preempt_timer);
> > + struct msm_gpu *gpu = &a6xx_gpu->base.base;
> > + struct drm_device *dev = gpu->dev;
> > +
> > + if (!try_preempt_state(a6xx_gpu, PREEMPT_TRIGGERED, PREEMPT_FAULTED))
> > + return;
> > +
> > + dev_err(dev->dev, "%s: preemption timed out\n", gpu->name);
> > + kthread_queue_work(gpu->worker, &gpu->recover_work);
> > +}
> > +
> > +void a6xx_preempt_irq(struct msm_gpu *gpu)
> > +{
> > + uint32_t status;
> > + struct adreno_gpu *adreno_gpu = to_adreno_gpu(gpu);
> > + struct a6xx_gpu *a6xx_gpu = to_a6xx_gpu(adreno_gpu);
> > + struct drm_device *dev = gpu->dev;
> > +
> > + if (!try_preempt_state(a6xx_gpu, PREEMPT_TRIGGERED, PREEMPT_PENDING))
> > + return;
> > +
> > + /* Delete the preemption watchdog timer */
> > + del_timer(&a6xx_gpu->preempt_timer);
> > +
> > + /*
> > + * The hardware should be setting the stop bit of CP_CONTEXT_SWITCH_CNTL
> > + * to zero before firing the interrupt, but there is a non zero chance
> > + * of a hardware condition or a software race that could set it again
> > + * before we have a chance to finish. If that happens, log and go for
> > + * recovery
> > + */
> > + status = gpu_read(gpu, REG_A6XX_CP_CONTEXT_SWITCH_CNTL);
> > + if (unlikely(status & A6XX_CP_CONTEXT_SWITCH_CNTL_STOP)) {
> > + DRM_DEV_ERROR(&gpu->pdev->dev,
> > + "!!!!!!!!!!!!!!!! preemption faulted !!!!!!!!!!!!!! irq\n");
> > + set_preempt_state(a6xx_gpu, PREEMPT_FAULTED);
> > + dev_err(dev->dev, "%s: Preemption failed to complete\n",
> > + gpu->name);
> > + kthread_queue_work(gpu->worker, &gpu->recover_work);
> > + return;
> > + }
> > +
> > + a6xx_gpu->cur_ring = a6xx_gpu->next_ring;
> > + a6xx_gpu->next_ring = NULL;
> > +
> > + /* Make sure the write to cur_ring is posted before the change in state */
> > + wmb();
>
> Not needed. set_preempt_state has the necessary barrier.
>
> > +
> > + set_preempt_state(a6xx_gpu, PREEMPT_FINISH);
> > +
> > + update_wptr(gpu, a6xx_gpu->cur_ring);
> > +
> > + set_preempt_state(a6xx_gpu, PREEMPT_NONE);
> > +
> > + /*
> > + * Retrigger preemption to avoid a deadlock that might occur when preemption
> > + * is skipped due to it being already in flight when requested.
> > + */
> > + a6xx_preempt_trigger(gpu);
> > +}
> > +
> > +void a6xx_preempt_hw_init(struct msm_gpu *gpu)
> > +{
> > + struct adreno_gpu *adreno_gpu = to_adreno_gpu(gpu);
> > + struct a6xx_gpu *a6xx_gpu = to_a6xx_gpu(adreno_gpu);
> > + int i;
> > +
> > + /* No preemption if we only have one ring */
> > + if (gpu->nr_rings == 1)
> > + return;
> > +
> > + for (i = 0; i < gpu->nr_rings; i++) {
> > + struct a6xx_preempt_record *record_ptr =
> > + a6xx_gpu->preempt[i] + PREEMPT_OFFSET_PRIV_NON_SECURE;
> > + record_ptr->wptr = 0;
> > + record_ptr->rptr = 0;
> > + record_ptr->rptr_addr = shadowptr(a6xx_gpu, gpu->rb[i]);
> > + record_ptr->info = 0;
> > + record_ptr->data = 0;
> > + record_ptr->rbase = gpu->rb[i]->iova;
> > + }
> > +
> > + /* Write a 0 to signal that we aren't switching pagetables */
> > + gpu_write64(gpu, REG_A6XX_CP_CONTEXT_SWITCH_SMMU_INFO, 0);
> > +
> > + /* Enable the GMEM save/restore feature for preemption */
> > + gpu_write(gpu, REG_A6XX_RB_CONTEXT_SWITCH_GMEM_SAVE_RESTORE, 0x1);
> > +
> > + /* Reset the preemption state */
> > + set_preempt_state(a6xx_gpu, PREEMPT_NONE);
> > +
> > + spin_lock_init(&a6xx_gpu->eval_lock);
> > +
> > + /* Always come up on rb 0 */
> > + a6xx_gpu->cur_ring = gpu->rb[0];
> > +}
> > +
> > +void a6xx_preempt_trigger(struct msm_gpu *gpu)
> > +{
> > + struct adreno_gpu *adreno_gpu = to_adreno_gpu(gpu);
> > + struct a6xx_gpu *a6xx_gpu = to_a6xx_gpu(adreno_gpu);
> > + u64 preempt_offset_priv_secure;
> > + unsigned long flags;
> > + struct msm_ringbuffer *ring;
> > + unsigned int cntl;
> > +
> > + if (gpu->nr_rings == 1)
> > + return;
> > +
> > + /*
> > + * Lock to make sure another thread attempting preemption doesn't skip it
> > + * while we are still evaluating the next ring. This makes sure the other
> > + * thread does start preemption if we abort it and avoids a soft lock.
> > + */
> > + spin_lock_irqsave(&a6xx_gpu->eval_lock, flags);
> > +
> > + /*
> > + * Try to start preemption by moving from NONE to START. If
> > + * unsuccessful, a preemption is already in flight
> > + */
> > + if (!try_preempt_state(a6xx_gpu, PREEMPT_NONE, PREEMPT_START)) {
> > + spin_unlock_irqrestore(&a6xx_gpu->eval_lock, flags);
> > + return;
> > + }
> > +
> > + cntl = A6XX_CP_CONTEXT_SWITCH_CNTL_LEVEL(a6xx_gpu->preempt_level);
> > +
> > + if (a6xx_gpu->skip_save_restore)
> > + cntl |= A6XX_CP_CONTEXT_SWITCH_CNTL_SKIP_SAVE_RESTORE;
> > +
> > + if (a6xx_gpu->uses_gmem)
> > + cntl |= A6XX_CP_CONTEXT_SWITCH_CNTL_USES_GMEM;
> > +
> > + cntl |= A6XX_CP_CONTEXT_SWITCH_CNTL_STOP;
> > +
> > + /* Get the next ring to preempt to */
> > + ring = get_next_ring(gpu);
> > +
> > + /*
> > + * If no ring is populated or the highest priority ring is the current
> > + * one do nothing except to update the wptr to the latest and greatest
> > + */
> > + if (!ring || (a6xx_gpu->cur_ring == ring)) {
> > + set_preempt_state(a6xx_gpu, PREEMPT_FINISH);
> > + update_wptr(gpu, a6xx_gpu->cur_ring);
> > + set_preempt_state(a6xx_gpu, PREEMPT_NONE);
> > + spin_unlock_irqrestore(&a6xx_gpu->eval_lock, flags);
> > + return;
> > + }
> > +
> > + spin_unlock_irqrestore(&a6xx_gpu->eval_lock, flags);
> > +
> > + spin_lock_irqsave(&ring->preempt_lock, flags);
> > +
> > + struct a7xx_cp_smmu_info *smmu_info_ptr =
> > + a6xx_gpu->preempt[ring->id] + PREEMPT_OFFSET_SMMU_INFO;
> > + struct a6xx_preempt_record *record_ptr =
> > + a6xx_gpu->preempt[ring->id] + PREEMPT_OFFSET_PRIV_NON_SECURE;
> > + u64 ttbr0 = ring->memptrs->ttbr0;
> > + u32 context_idr = ring->memptrs->context_idr;
> > +
> > + smmu_info_ptr->ttbr0 = ttbr0;
> > + smmu_info_ptr->context_idr = context_idr;
> > + record_ptr->wptr = get_wptr(ring);
> > +
> > + /*
> > + * The GPU will write the wptr we set above when we preempt. Reset
> > + * skip_inline_wptr to make sure that we don't write WPTR to the same
> > + * thing twice. It's still possible subsequent submissions will update
> > + * wptr again, in which case they will set the flag to true. This has
> > + * to be protected by the lock for setting the flag and updating wptr
> > + * to be atomic.
> > + */
> > + ring->skip_inline_wptr = false;
> > +
> > + spin_unlock_irqrestore(&ring->preempt_lock, flags);
> > +
> > + gpu_write64(gpu,
> > + REG_A6XX_CP_CONTEXT_SWITCH_SMMU_INFO,
> > + a6xx_gpu->preempt_iova[ring->id] + PREEMPT_OFFSET_SMMU_INFO);
> > +
> > + gpu_write64(gpu,
> > + REG_A6XX_CP_CONTEXT_SWITCH_PRIV_NON_SECURE_RESTORE_ADDR,
> > + a6xx_gpu->preempt_iova[ring->id] + PREEMPT_OFFSET_PRIV_NON_SECURE);
> > +
> > + preempt_offset_priv_secure =
> > + PREEMPT_OFFSET_PRIV_SECURE(adreno_gpu->info->preempt_record_size);
> > + gpu_write64(gpu,
> > + REG_A6XX_CP_CONTEXT_SWITCH_PRIV_SECURE_RESTORE_ADDR,
> > + a6xx_gpu->preempt_iova[ring->id] + preempt_offset_priv_secure);
>
> Secure buffers are not supported currently, so we can skip this and the
> context record allocation. Anyway this has to be a separate buffer
> mapped in secure pagetable which don't currently have. We can skip the
> same in pseudo register packet too.
>
> > +
> > + a6xx_gpu->next_ring = ring;
> > +
> > + /* Start a timer to catch a stuck preemption */
> > + mod_timer(&a6xx_gpu->preempt_timer, jiffies + msecs_to_jiffies(10000));
> > +
> > + /* Set the preemption state to triggered */
> > + set_preempt_state(a6xx_gpu, PREEMPT_TRIGGERED);
> > +
> > + /* Make sure any previous writes to WPTR are posted */
> > + gpu_read(gpu, REG_A6XX_CP_RB_WPTR);
> > +
> > + /* Make sure everything is written before hitting the button */
> > + wmb();
>
> This and the above read back looks unnecessary. All writes to gpu are
> ordered anyway.
I thought the whole reason for
https://lore.kernel.org/linux-kernel/20240508-topic-adreno-v1-1-1babd05c119d@xxxxxxxxxx/
is that memory-mapped writes to different GPU registers are *not*
necessarily ordered from the GPU's perspective (even if they are from
the CPU). That's why I suggested the readback. Or am I missing
something?
>
> > +
> > + /* Trigger the preemption */
> > + gpu_write(gpu, REG_A6XX_CP_CONTEXT_SWITCH_CNTL, cntl);
> > +}
> > +
> > +static int preempt_init_ring(struct a6xx_gpu *a6xx_gpu,
> > + struct msm_ringbuffer *ring)
> > +{
> > + struct adreno_gpu *adreno_gpu = &a6xx_gpu->base;
> > + struct msm_gpu *gpu = &adreno_gpu->base;
> > + struct drm_gem_object *bo = NULL;
> > + phys_addr_t ttbr;
> > + u64 iova = 0;
> > + void *ptr;
> > + int asid;
> > +
> > + ptr = msm_gem_kernel_new(gpu->dev,
> > + PREEMPT_SIZE(adreno_gpu->info->preempt_record_size),
> > + MSM_BO_WC | MSM_BO_MAP_PRIV, gpu->aspace, &bo, &iova);
>
> set a name?
>
> > +
> > + memset(ptr, 0, PREEMPT_SIZE(adreno_gpu->info->preempt_record_size));
> > +
> > + if (IS_ERR(ptr))
> > + return PTR_ERR(ptr);
> > +
> > + a6xx_gpu->preempt_bo[ring->id] = bo;
> > + a6xx_gpu->preempt_iova[ring->id] = iova;
> > + a6xx_gpu->preempt[ring->id] = ptr;
> > +
> > + struct a7xx_cp_smmu_info *smmu_info_ptr = ptr + PREEMPT_OFFSET_SMMU_INFO;
> > + struct a6xx_preempt_record *record_ptr = ptr + PREEMPT_OFFSET_PRIV_NON_SECURE;
> > +
> > + msm_iommu_pagetable_params(gpu->aspace->mmu, &ttbr, &asid);
> > +
> > + smmu_info_ptr->magic = GEN7_CP_SMMU_INFO_MAGIC;
> > + smmu_info_ptr->ttbr0 = ttbr;
> > + smmu_info_ptr->asid = 0xdecafbad;
> > + smmu_info_ptr->context_idr = 0;
> > +
> > + /* Set up the defaults on the preemption record */
> > + record_ptr->magic = A6XX_PREEMPT_RECORD_MAGIC;
> > + record_ptr->info = 0;
> > + record_ptr->data = 0;
> > + record_ptr->rptr = 0;
> > + record_ptr->wptr = 0;
> > + record_ptr->cntl = MSM_GPU_RB_CNTL_DEFAULT;
> > + record_ptr->rbase = ring->iova;
> > + record_ptr->counter = 0;
> > + record_ptr->bv_rptr_addr = rbmemptr(ring, bv_rptr);
> > +
> > + return 0;
> > +}
> > +
> > +void a6xx_preempt_fini(struct msm_gpu *gpu)
> > +{
> > + struct adreno_gpu *adreno_gpu = to_adreno_gpu(gpu);
> > + struct a6xx_gpu *a6xx_gpu = to_a6xx_gpu(adreno_gpu);
> > + int i;
> > +
> > + for (i = 0; i < gpu->nr_rings; i++)
> > + msm_gem_kernel_put(a6xx_gpu->preempt_bo[i], gpu->aspace);
> > +}
> > +
> > +void a6xx_preempt_init(struct msm_gpu *gpu)
> > +{
> > + struct adreno_gpu *adreno_gpu = to_adreno_gpu(gpu);
> > + struct a6xx_gpu *a6xx_gpu = to_a6xx_gpu(adreno_gpu);
> > + int i;
> > +
> > + /* No preemption if we only have one ring */
> > + if (gpu->nr_rings <= 1)
> > + return;
> > +
> > + for (i = 0; i < gpu->nr_rings; i++) {
> > + if (preempt_init_ring(a6xx_gpu, gpu->rb[i]))
> > + goto fail;
> > + }
> > +
> > + /* TODO: make this configurable? */
> > + a6xx_gpu->preempt_level = 1;
> > + a6xx_gpu->uses_gmem = 1;
> > + a6xx_gpu->skip_save_restore = 1;
> > +
> > + timer_setup(&a6xx_gpu->preempt_timer, a6xx_preempt_timer, 0);
> > +
> > + return;
> > +fail:
>
> Log an error so that preemption is not disabled silently?
>
> > + /*
> > + * On any failure our adventure is over. Clean up and
> > + * set nr_rings to 1 to force preemption off
> > + */
> > + a6xx_preempt_fini(gpu);
> > + gpu->nr_rings = 1;
> > +
> > + return;
> > +}
> > diff --git a/drivers/gpu/drm/msm/msm_ringbuffer.h b/drivers/gpu/drm/msm/msm_ringbuffer.h
> > index 40791b2ade46..7dde6a312511 100644
> > --- a/drivers/gpu/drm/msm/msm_ringbuffer.h
> > +++ b/drivers/gpu/drm/msm/msm_ringbuffer.h
> > @@ -36,6 +36,7 @@ struct msm_rbmemptrs {
> >
> > volatile struct msm_gpu_submit_stats stats[MSM_GPU_SUBMIT_STATS_COUNT];
> > volatile u64 ttbr0;
> > + volatile u32 context_idr;
> > };
> >
> > struct msm_cp_state {
> > @@ -100,6 +101,12 @@ struct msm_ringbuffer {
> > * preemption. Can be aquired from irq context.
> > */
> > spinlock_t preempt_lock;
> > +
> > + /*
> > + * Whether we skipped writing wptr and it needs to be updated in the
> > + * future when the ring becomes current.
> > + */
> > + bool skip_inline_wptr;
>
> nit: does 'restore_wptr' makes more sense? Or something better? Basically, name it based
> on the future action?
>
> -Akhil
>
> > };
> >
> > struct msm_ringbuffer *msm_ringbuffer_new(struct msm_gpu *gpu, int id,
> >
> > --
> > 2.46.0
> >