Message-ID: <f6a643dd-b835-adbf-6a06-ea3843fa8f12@arm.com>
Date:   Tue, 6 Feb 2018 16:23:03 +0000
From:   Marc Zyngier <marc.zyngier@....com>
To:     "dbasehore ." <dbasehore@...omium.org>
Cc:     linux-kernel <linux-kernel@...r.kernel.org>,
        Soby Mathew <Soby.Mathew@....com>,
        Sudeep Holla <sudeep.holla@....com>,
        devicetree@...r.kernel.org, robh+dt@...nel.org,
        Mark Rutland <mark.rutland@....com>,
        Linux-pm mailing list <linux-pm@...r.kernel.org>,
        "Wysocki, Rafael J" <rafael.j.wysocki@...el.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Brian Norris <briannorris@...omium.org>
Subject: Re: [PATCH v4 2/5] irqchip/gic-v3-its: add ability to save/restore
 ITS state

On 05/02/18 21:33, dbasehore . wrote:
> On Mon, Feb 5, 2018 at 7:56 AM, Marc Zyngier <marc.zyngier@....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@...omium.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.
> 
> Sounds reasonable. I think I just have it this way because I used to
> have more in here.
> 
>>
>>> +
>>>  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?
> 
> CREADR is RO and we need to handle the non-zero case. I was planning
> on getting rid of the write to CWRITER since it shouldn't be needed.
> Either CREADR and CWRITER have the prior values, or both are reset to
> 0.

You're writing GITS_CBASER, which has for consequence: "When this
register is successfully written, the value of GITS_CREADR is set to
zero.". Ergo, none of that is necessary and you *must* set CWRITER to 0.

> 
>>
>>> +                     /* 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.
>>
>>> +                     }
>>> +                     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?
> 
> The save_disable code put it in a disabled state. The reset state is> also disabled. I don't expect PSCI to change the GITS_CTLR register at
> all. Are you expecting something on the other side of the PSCI layer
> to poke this register? We'd probably want to force disable at the
> start of restore_enable if so.

I expect firmware to do its worse, because even if mainline ATF is close
to perfection, it will be hacked to death by platform people who usually
do not have a clue (that's definitely my experience). So I expect this
code to be written defensively.

Thanks,

	M.
-- 
Jazz is not dead. It just smells funny...

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