Re: [PATCH v6] drm/msm/a6xx: Add support for an interconnect path

[Evan Green]

On Fri, Jan 18, 2019 at 3:27 PM Jordan Crouse <jcrouse@xxxxxxxxxxxxxx> wrote:
>
> On Fri, Jan 18, 2019 at 03:04:34PM -0800, Evan Green wrote:
> > On Fri, Jan 18, 2019 at 12:24 PM Jordan Crouse <jcrouse@xxxxxxxxxxxxxx> wrote:
> > >
> > > Try to get the interconnect path for the GPU and vote for the maximum
> > > bandwidth to support all frequencies. This is needed for performance.
> > > Later we will want to scale the bandwidth based on the frequency to
> > > also optimize for power but that will require some device tree
> > > infrastructure that does not yet exist.
> > >
> > > v6: use icc_set_bw() instead of icc_set()
> > > v5: Remove hardcoded interconnect name and just use the default
> > > v4: Don't use a port string at all to skip the need for names in the DT
> > > v3: Use macros and change port string per Georgi Djakov
> > >
> > > Signed-off-by: Jordan Crouse <jcrouse@xxxxxxxxxxxxxx>
> > > ---
> > >
> > >  drivers/gpu/drm/msm/Kconfig             |  1 +
> > >  drivers/gpu/drm/msm/adreno/a6xx_gmu.c   | 20 ++++++++++++++++++++
> > >  drivers/gpu/drm/msm/adreno/adreno_gpu.c |  9 +++++++++
> > >  drivers/gpu/drm/msm/msm_gpu.h           |  3 +++
> > >  4 files changed, 33 insertions(+)
> > >
> > > diff --git a/drivers/gpu/drm/msm/Kconfig b/drivers/gpu/drm/msm/Kconfig
> > > index cf549f1..78c9e5a5 100644
> > > --- a/drivers/gpu/drm/msm/Kconfig
> > > +++ b/drivers/gpu/drm/msm/Kconfig
> > > @@ -5,6 +5,7 @@ config DRM_MSM
> > >         depends on ARCH_QCOM || SOC_IMX5 || (ARM && COMPILE_TEST)
> > >         depends on OF && COMMON_CLK
> > >         depends on MMU
> > > +       depends on INTERCONNECT || !INTERCONNECT
> > >         select QCOM_MDT_LOADER if ARCH_QCOM
> > >         select REGULATOR
> > >         select DRM_KMS_HELPER
> > > diff --git a/drivers/gpu/drm/msm/adreno/a6xx_gmu.c b/drivers/gpu/drm/msm/adreno/a6xx_gmu.c
> > > index 5beb83d..c48fe46 100644
> > > --- a/drivers/gpu/drm/msm/adreno/a6xx_gmu.c
> > > +++ b/drivers/gpu/drm/msm/adreno/a6xx_gmu.c
> > > @@ -2,6 +2,7 @@
> > >  /* Copyright (c) 2017-2018 The Linux Foundation. All rights reserved. */
> > >
> > >  #include <linux/clk.h>
> > > +#include <linux/interconnect.h>
> > >  #include <linux/pm_opp.h>
> > >  #include <soc/qcom/cmd-db.h>
> > >
> > > @@ -84,6 +85,9 @@ bool a6xx_gmu_gx_is_on(struct a6xx_gmu *gmu)
> > >
> > >  static void __a6xx_gmu_set_freq(struct a6xx_gmu *gmu, int index)
> > >  {
> > > +       struct a6xx_gpu *a6xx_gpu = container_of(gmu, struct a6xx_gpu, gmu);
> > > +       struct adreno_gpu *adreno_gpu = &a6xx_gpu->base;
> > > +       struct msm_gpu *gpu = &adreno_gpu->base;
> > >         int ret;
> > >
> > >         gmu_write(gmu, REG_A6XX_GMU_DCVS_ACK_OPTION, 0);
> > > @@ -106,6 +110,12 @@ static void __a6xx_gmu_set_freq(struct a6xx_gmu *gmu, int index)
> > >                 dev_err(gmu->dev, "GMU set GPU frequency error: %d\n", ret);
> > >
> > >         gmu->freq = gmu->gpu_freqs[index];
> > > +
> > > +       /*
> > > +        * Eventually we will want to scale the path vote with the frequency but
> > > +        * for now leave it at max so that the performance is nominal.
> > > +        */
> > > +       icc_set_bw(gpu->icc_path, 0, MBps_to_icc(7216));
> > >  }
> > >
> > >  void a6xx_gmu_set_freq(struct msm_gpu *gpu, unsigned long freq)
> > > @@ -705,6 +715,8 @@ int a6xx_gmu_reset(struct a6xx_gpu *a6xx_gpu)
> > >
> > >  int a6xx_gmu_resume(struct a6xx_gpu *a6xx_gpu)
> > >  {
> > > +       struct adreno_gpu *adreno_gpu = &a6xx_gpu->base;
> > > +       struct msm_gpu *gpu = &adreno_gpu->base;
> > >         struct a6xx_gmu *gmu = &a6xx_gpu->gmu;
> > >         int status, ret;
> > >
> > > @@ -720,6 +732,9 @@ int a6xx_gmu_resume(struct a6xx_gpu *a6xx_gpu)
> > >         if (ret)
> > >                 goto out;
> > >
> > > +       /* Set the bus quota to a reasonable value for boot */
> > > +       icc_set_bw(gpu->icc_path, 0, MBps_to_icc(3072));
> >
> > Does the comment mention boot because this resume call happens during
> > init?
>
> Correct. Boot refers to the GMU in this context.
>
> > How come this number is different from the one in __a6xx_gmu_set_freq?
>
> If you never request a bus quota from the kernel the sucker is horribly
> painfully slow. I'm not sure if that is just the default reset value of
> the registers or if the bootloader is doing something. In any event
> the GMU doesn't always initialize if you try to bring it up with the
> default bus settings so we set it to a "reasonable" quota for the
> init sequence. I admit I didn't come up with these numbers on my own;
> some poor anonymous soul debugged this on the downstream kernel and
> I just stole the same parameters.
>
> As for _a6xx_gmu_set_freq() eventually we'll agree on a way to communicate
> the bus bandwidth in the opp settings and we'll be able to adjust the quota
> based on the frequency to save power so that's why the code is organized the way
> it is so that a6xx_gmu_set_freq() won't have to be massively changed later.

Oh I see, so it's just a placeholder to max for now until the OPP part
gets figured out. That makes sense.

Reviewed-by: Evan Green <evgreen@xxxxxxxxxxxx>