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

["dbasehore ." <dbasehore@chromium.org>]

On Mon, Feb 5, 2018 at 5:01 PM, dbasehore . <dbasehore@chromium.org> wrote:
> On Mon, Feb 5, 2018 at 4:33 PM, dbasehore . <dbasehore@chromium.org> wrote:
>> On Mon, Feb 5, 2018 at 7:56 AM, Marc Zyngier <marc.zyngier@arm.com> 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@chromium.org>
>>>> ---
>>>>  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.
>>
>
> Okay, I found this snippet in the GICv3 Specification:
> No memory is allocated for the translation table. The ITS discards any
> writes to the
> interrupt translation page when either:
> • GITS_BASER<n>.Type specifies any valid table entry type other than interrupt
> collections, that is, any value other than 100.
> • GITS_BASER<n>.Type specifies an interrupt collection and
> GITS_TYPER.HCC == 0.

This is when GITS_BASER.Valid == 0 by the way.

>
> I'll turn this into a test in code and only write the BASER if that passes.
>
>>>> +                     }
>>>> +                     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...