Re: [PATCH v4 2/5] irqchip/gic-v3-its: add ability to save/restore ITS state

From: dbasehore .
Date: Mon Feb 05 2018 - 19:33:47 EST

On Mon, Feb 5, 2018 at 7:56 AM, Marc Zyngier <marc.zyngier@xxxxxxx> wrote:
> On 03/02/18 01:24, Derek Basehore wrote:
>> Some platforms power off GIC logic in suspend, so we need to
>> save/restore state. The distributor and redistributor registers need
>> to be handled in platform code due to access permissions on those
>> registers, but the ITS registers can be restored in the kernel.
>>
>> Signed-off-by: Derek Basehore <dbasehore@xxxxxxxxxxxx>
>> ---
>> drivers/irqchip/irq-gic-v3-its.c | 101 +++++++++++++++++++++++++++++++++++++++
>> 1 file changed, 101 insertions(+)
>>
>> diff --git a/drivers/irqchip/irq-gic-v3-its.c b/drivers/irqchip/irq-gic-v3-its.c
>> index 06f025fd5726..e13515cdb68f 100644
>> --- a/drivers/irqchip/irq-gic-v3-its.c
>> +++ b/drivers/irqchip/irq-gic-v3-its.c
>> @@ -33,6 +33,7 @@
>> #include <linux/of_platform.h>
>> #include <linux/percpu.h>
>> #include <linux/slab.h>
>> +#include <linux/syscore_ops.h>
>>
>> #include <linux/irqchip.h>
>> #include <linux/irqchip/arm-gic-v3.h>
>> @@ -46,6 +47,7 @@
>> #define ITS_FLAGS_CMDQ_NEEDS_FLUSHING (1ULL << 0)
>> #define ITS_FLAGS_WORKAROUND_CAVIUM_22375 (1ULL << 1)
>> #define ITS_FLAGS_WORKAROUND_CAVIUM_23144 (1ULL << 2)
>> +#define ITS_FLAGS_SAVE_SUSPEND_STATE (1ULL << 3)
>>
>> #define RDIST_FLAGS_PROPBASE_NEEDS_FLUSHING (1 << 0)
>>
>> @@ -83,6 +85,15 @@ struct its_baser {
>> u32 psz;
>> };
>>
>> +/*
>> + * Saved ITS state - this is where saved state for the ITS is stored
>> + * when it's disabled during system suspend.
>> + */
>> +struct its_ctx {
>> + u64 cbaser;
>> + u32 ctlr;
>> +};
>
> Nit: This is pretty small for the ITS context. Given that its_node is
> the context, you can safely expand this in the its_node structure.
>
>> +
>> struct its_device;
>>
>> /*
>> @@ -101,6 +112,7 @@ struct its_node {
>> struct its_collection *collections;
>> struct fwnode_handle *fwnode_handle;
>> u64 (*get_msi_base)(struct its_device *its_dev);
>> + struct its_ctx its_ctx;
>> struct list_head its_device_list;
>> u64 flags;
>> unsigned long list_nr;
>> @@ -3042,6 +3054,90 @@ static void its_enable_quirks(struct its_node *its)
>> gic_enable_quirks(iidr, its_quirks, its);
>> }
>>
>> +static int its_save_disable(void)
>> +{
>> + struct its_node *its;
>> + int err = 0;
>> +
>> + spin_lock(&its_lock);
>> + list_for_each_entry(its, &its_nodes, entry) {
>> + struct its_ctx *ctx;
>> + void __iomem *base;
>> +
>> + if (!(its->flags & ITS_FLAGS_SAVE_SUSPEND_STATE))
>> + continue;
>> +
>> + ctx = &its->its_ctx;
>> + base = its->base;
>> + ctx->ctlr = readl_relaxed(base + GITS_CTLR);
>> + err = its_force_quiescent(base);
>> + if (err) {
>> + pr_err("ITS failed to quiesce\n");
>> + writel_relaxed(ctx->ctlr, base + GITS_CTLR);
>> + goto err;
>> + }
>> +
>> + ctx->cbaser = gits_read_cbaser(base + GITS_CBASER);
>> + }
>> +
>> +err:
>> + if (err) {
>> + list_for_each_entry_continue_reverse(its, &its_nodes, entry) {
>> + if (its->flags & ITS_FLAGS_SAVE_SUSPEND_STATE) {
>> + struct its_ctx *ctx = &its->its_ctx;
>> + void __iomem *base = its->base;
>> +
>> + writel_relaxed(ctx->ctlr, base + GITS_CTLR);
>> + }
>> + }
>> + }
>> +
>> + spin_unlock(&its_lock);
>> +
>> + return err;
>> +}
>> +
>> +static void its_restore_enable(void)
>> +{
>> + struct its_node *its;
>> +
>> + spin_lock(&its_lock);
>> + list_for_each_entry(its, &its_nodes, entry) {
>> + if (its->flags & ITS_FLAGS_SAVE_SUSPEND_STATE) {
>> + struct its_ctx *ctx = &its->its_ctx;
>> + void __iomem *base = its->base;
>> + /*
>> + * Only the lower 32 bits matter here since the upper 32
>> + * don't include any of the offset.
>> + */
>> + u32 creader = readl_relaxed(base + GITS_CREADR);
>
> Accessor matching gits_write_cwriter and co?
>
>> + int i;
>> +
>> + /*
>> + * Reset the write location to where the ITS is
>> + * currently at.
>> + */
>> + gits_write_cbaser(ctx->cbaser, base + GITS_CBASER);
>> + gits_write_cwriter(creader, base + GITS_CWRITER);
>> + its->cmd_write = &its->cmd_base[
>> + creader / sizeof(struct its_cmd_block)];
>
> Nit: please do not split lines like this, this is unreadable. We both
> have screens that are wide enough for this to fit on a single line.
>
> More importantly: Why isn't it sufficient to reset both CREADR and
> CWRITER to zero? Is there any case where you can suspend whilst having
> anything in flight?
>
>> + /* Restore GITS_BASER from the value cache. */
>> + for (i = 0; i < GITS_BASER_NR_REGS; i++) {
>> + struct its_baser *baser = &its->tables[i];
>> +
>> + its_write_baser(its, baser, baser->val);
>
> You may want to first test that this BASER register is actually
> requiring something before writing to it. Yes, this is normally safe.
> But HW is also normally broken.
>

Anything specific to test? I see that I can check if the BASER
register has the valid bit set and also that the type is not none.

>> + }
>> + writel_relaxed(ctx->ctlr, base + GITS_CTLR);
>
> Before restoring all of this, shouldn't you first test that the ITS is
> actually in a disabled state?
>
>> + }
>> + }
>> + spin_unlock(&its_lock);
>> +}
>> +
>> +static struct syscore_ops its_syscore_ops = {
>> + .suspend = its_save_disable,
>> + .resume = its_restore_enable,
>> +};
>> +
>> static int its_init_domain(struct fwnode_handle *handle, struct its_node *its)
>> {
>> struct irq_domain *inner_domain;
>> @@ -3261,6 +3357,9 @@ static int __init its_probe_one(struct resource *res,
>> ctlr |= GITS_CTLR_ImDe;
>> writel_relaxed(ctlr, its->base + GITS_CTLR);
>>
>> + if (fwnode_property_present(handle, "reset-on-suspend"))
>> + its->flags |= ITS_FLAGS_SAVE_SUSPEND_STATE;
>> +
>> err = its_init_domain(handle, its);
>> if (err)
>> goto out_free_tables;
>> @@ -3515,5 +3614,7 @@ int __init its_init(struct fwnode_handle *handle, struct rdists *rdists,
>> }
>> }
>>
>> + register_syscore_ops(&its_syscore_ops);
>> +
>> return 0;
>> }
>>
>
> Thanks,
>
> M.
> --
> Jazz is not dead. It just smells funny...