Message-Id: <20180711134054eucas1p208566383b25dd74787034929b3081901~AVDO-rPhL2314323143eucas1p2n@eucas1p2.samsung.com>
Date:   Wed, 11 Jul 2018 15:40:53 +0200
From:   Marek Szyprowski <m.szyprowski@...sung.com>
To:     Tomasz Figa <tfiga@...omium.org>, rafael@...nel.org,
        Vivek Gautam <vivek.gautam@...eaurora.org>
Cc:     "Rafael J. Wysocki" <rjw@...ysocki.net>,
        "list@....net:IOMMU DRIVERS" <iommu@...ts.linux-foundation.org>,
        Joerg Roedel <joro@...tes.org>, joro@...tes.org,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Robin Murphy <robin.murphy@....com>,
        Will Deacon <will.deacon@....com>,
        "list@....net:IOMMU DRIVERS" <iommu@...ts.linux-foundation.org>,
        Joerg Roedel <joro@...tes.org>,
        iommu@...ts.linux-foundation.org, devicetree@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Alex Williamson <alex.williamson@...hat.com>,
        Rob Clark <robdclark@...il.com>,
        Linux PM <linux-pm@...r.kernel.org>,
        freedreno <freedreno@...ts.freedesktop.org>, sboyd@...nel.org,
        Sricharan R <sricharan@...eaurora.org>,
        Archit Taneja <architt@...eaurora.org>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        jcrouse@...eaurora.org
Subject: Re: [PATCH v12 1/4] iommu/arm-smmu: Add pm_runtime/sleep ops

Hi Tomasz,

On 2018-07-11 14:51, Tomasz Figa wrote:
> On Wed, Jul 11, 2018 at 8:11 PM Rafael J. Wysocki <rafael@...nel.org> wrote:
>> On Wed, Jul 11, 2018 at 12:55 PM, Vivek Gautam
>> <vivek.gautam@...eaurora.org> wrote:
>>> On Wed, Jul 11, 2018 at 3:20 PM, Rafael J. Wysocki <rjw@...ysocki.net> wrote:
>>>> On Sunday, July 8, 2018 7:34:10 PM CEST Vivek Gautam wrote:
>>>>> From: Sricharan R <sricharan@...eaurora.org>
>>>>>
>>>>> The smmu needs to be functional only when the respective
>>>>> master's using it are active. The device_link feature
>>>>> helps to track such functional dependencies, so that the
>>>>> iommu gets powered when the master device enables itself
>>>>> using pm_runtime. So by adapting the smmu driver for
>>>>> runtime pm, above said dependency can be addressed.
>>>>>
>>>>> This patch adds the pm runtime/sleep callbacks to the
>>>>> driver and also the functions to parse the smmu clocks
>>>>> from DT and enable them in resume/suspend.
>>>>>
>>>>> Signed-off-by: Sricharan R <sricharan@...eaurora.org>
>>>>> Signed-off-by: Archit Taneja <architt@...eaurora.org>
>>>>> [vivek: Clock rework to request bulk of clocks]
>>>>> Signed-off-by: Vivek Gautam <vivek.gautam@...eaurora.org>
>>>>> Reviewed-by: Tomasz Figa <tfiga@...omium.org>
>>>>> ---
>>>>>
>>>>>   - No change since v11.
>>>>>
>>>>>   drivers/iommu/arm-smmu.c | 60 ++++++++++++++++++++++++++++++++++++++++++++++--
>>>>>   1 file changed, 58 insertions(+), 2 deletions(-)
>>>>>
>>>>> diff --git a/drivers/iommu/arm-smmu.c b/drivers/iommu/arm-smmu.c
>>>>> index f7a96bcf94a6..a01d0dde21dd 100644
>>>>> --- a/drivers/iommu/arm-smmu.c
>>>>> +++ b/drivers/iommu/arm-smmu.c
>>>>> @@ -48,6 +48,7 @@
>>>>>   #include <linux/of_iommu.h>
>>>>>   #include <linux/pci.h>
>>>>>   #include <linux/platform_device.h>
>>>>> +#include <linux/pm_runtime.h>
>>>>>   #include <linux/slab.h>
>>>>>   #include <linux/spinlock.h>
>>>>>
>>>>> @@ -205,6 +206,8 @@ struct arm_smmu_device {
>>>>>        u32                             num_global_irqs;
>>>>>        u32                             num_context_irqs;
>>>>>        unsigned int                    *irqs;
>>>>> +     struct clk_bulk_data            *clks;
>>>>> +     int                             num_clks;
>>>>>
>>>>>        u32                             cavium_id_base; /* Specific to Cavium */
>>>>>
>>>>> @@ -1897,10 +1900,12 @@ static int arm_smmu_device_cfg_probe(struct arm_smmu_device *smmu)
>>>>>   struct arm_smmu_match_data {
>>>>>        enum arm_smmu_arch_version version;
>>>>>        enum arm_smmu_implementation model;
>>>>> +     const char * const *clks;
>>>>> +     int num_clks;
>>>>>   };
>>>>>
>>>>>   #define ARM_SMMU_MATCH_DATA(name, ver, imp)  \
>>>>> -static struct arm_smmu_match_data name = { .version = ver, .model = imp }
>>>>> +static const struct arm_smmu_match_data name = { .version = ver, .model = imp }
>>>>>
>>>>>   ARM_SMMU_MATCH_DATA(smmu_generic_v1, ARM_SMMU_V1, GENERIC_SMMU);
>>>>>   ARM_SMMU_MATCH_DATA(smmu_generic_v2, ARM_SMMU_V2, GENERIC_SMMU);
>>>>> @@ -1919,6 +1924,23 @@ static const struct of_device_id arm_smmu_of_match[] = {
>>>>>   };
>>>>>   MODULE_DEVICE_TABLE(of, arm_smmu_of_match);
>>>>>
>>>>> +static void arm_smmu_fill_clk_data(struct arm_smmu_device *smmu,
>>>>> +                                const char * const *clks)
>>>>> +{
>>>>> +     int i;
>>>>> +
>>>>> +     if (smmu->num_clks < 1)
>>>>> +             return;
>>>>> +
>>>>> +     smmu->clks = devm_kcalloc(smmu->dev, smmu->num_clks,
>>>>> +                               sizeof(*smmu->clks), GFP_KERNEL);
>>>>> +     if (!smmu->clks)
>>>>> +             return;
>>>>> +
>>>>> +     for (i = 0; i < smmu->num_clks; i++)
>>>>> +             smmu->clks[i].id = clks[i];
>>>>> +}
>>>>> +
>>>>>   #ifdef CONFIG_ACPI
>>>>>   static int acpi_smmu_get_data(u32 model, struct arm_smmu_device *smmu)
>>>>>   {
>>>>> @@ -2001,6 +2023,9 @@ static int arm_smmu_device_dt_probe(struct platform_device *pdev,
>>>>>        data = of_device_get_match_data(dev);
>>>>>        smmu->version = data->version;
>>>>>        smmu->model = data->model;
>>>>> +     smmu->num_clks = data->num_clks;
>>>>> +
>>>>> +     arm_smmu_fill_clk_data(smmu, data->clks);
>>>>>
>>>>>        parse_driver_options(smmu);
>>>>>
>>>>> @@ -2099,6 +2124,14 @@ static int arm_smmu_device_probe(struct platform_device *pdev)
>>>>>                smmu->irqs[i] = irq;
>>>>>        }
>>>>>
>>>>> +     err = devm_clk_bulk_get(smmu->dev, smmu->num_clks, smmu->clks);
>>>>> +     if (err)
>>>>> +             return err;
>>>>> +
>>>>> +     err = clk_bulk_prepare(smmu->num_clks, smmu->clks);
>>>>> +     if (err)
>>>>> +             return err;
>>>>> +
>>>>>        err = arm_smmu_device_cfg_probe(smmu);
>>>>>        if (err)
>>>>>                return err;
>>>>> @@ -2181,6 +2214,9 @@ static int arm_smmu_device_remove(struct platform_device *pdev)
>>>>>
>>>>>        /* Turn the thing off */
>>>>>        writel(sCR0_CLIENTPD, ARM_SMMU_GR0_NS(smmu) + ARM_SMMU_GR0_sCR0);
>>>>> +
>>>>> +     clk_bulk_unprepare(smmu->num_clks, smmu->clks);
>>>>> +
>>>>>        return 0;
>>>>>   }
>>>>>
>>>>> @@ -2197,7 +2233,27 @@ static int __maybe_unused arm_smmu_pm_resume(struct device *dev)
>>>>>        return 0;
>>>>>   }
>>>>>
>>>>> -static SIMPLE_DEV_PM_OPS(arm_smmu_pm_ops, NULL, arm_smmu_pm_resume);
>>>>> +static int __maybe_unused arm_smmu_runtime_resume(struct device *dev)
>>>>> +{
>>>>> +     struct arm_smmu_device *smmu = dev_get_drvdata(dev);
>>>>> +
>>>>> +     return clk_bulk_enable(smmu->num_clks, smmu->clks);
>>>>> +}
>>>>> +
>>>>> +static int __maybe_unused arm_smmu_runtime_suspend(struct device *dev)
>>>>> +{
>>>>> +     struct arm_smmu_device *smmu = dev_get_drvdata(dev);
>>>>> +
>>>>> +     clk_bulk_disable(smmu->num_clks, smmu->clks);
>>>>> +
>>>>> +     return 0;
>>>>> +}
>>>>> +
>>>>> +static const struct dev_pm_ops arm_smmu_pm_ops = {
>>>>> +     SET_SYSTEM_SLEEP_PM_OPS(NULL, arm_smmu_pm_resume)
>>>> This is suspicious.
>>>>
>>>> If you need a runtime suspend method, why do you think that it is not necessary
>>>> to suspend the device during system-wide transitions?
>>> Okay, so you suggest to put clock disabling in say arm_smmu_pm_suspend()?
>>> In that case the clocks have to be enabled in the resume path too.
>>>
>>> I remember Tomasz pointed to that we shouldn't need clock enable in resume
>>> path [1].
>>>
>>> [1] https://lkml.org/lkml/2018/3/15/60
> That was an answer for a different question. I don't remember
> suggesting having no suspend function. Although, given the PM
> subsystem internals, the suspend function wouldn't be called on SMMU
> implementation needed power control (since they would have runtime PM
> enabled) and on others, it would be called but do nothing (since no
> clocks).
>
>> Honestly, I just don't know. :-)
>>
>> It just looks odd the way it is done.  I think the clock should be
>> gated during system-wide suspend too, because the system can spend
>> much more time in a sleep state than in the working state, on average.
>>
>> And note that you cannot rely on runtime PM to always do it for you,
>> because it may be disabled at a client device or even blocked by user
>> space via power/control in sysfs and that shouldn't matter for
>> system-wide PM.
> User space blocking runtime PM through sysfs is a good point. I'm not
> 100% sure how the PM subsystem deals with that in case of system-wide
> suspend. I guess for consistency and safety, we should have the
> suspend callback.

Frankly, if there are no other reasons I suggest to wire system
suspend/resume to pm_runtime_force_* helpers:
SET_SYSTEM_SLEEP_PM_OPS(pm_runtime_force_suspend,
                         pm_runtime_force_resume).

This way you will have everything related to suspending and resuming in
one place and you would not need to bother about all possible cases (like
suspending from runtime pm active and suspending from runtime pm suspended
cases as well as restoring proper device state on resume). This is
especially important in recent kernel releases, where devices are
system-suspended regardless their runtime pm states (in older kernels
devices were first runtime resumed for system suspend, what made code
simpler, but wasn't best from power consumption perspective).

If you go this way, You only need to ensure that runtime resume will also
restore proper device state besides enabling all the clocks. This will
also prepare your driver to properly operate inside power domain, where it
is possible for device to loose its internal state after runtime suspend
when respective power domain has been turned off.

Best regards
-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland

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