Re: [PATCH v12 1/4] iommu/arm-smmu: Add pm_runtime/sleep ops

[Vivek Gautam <vivek.gautam@codeaurora.org>]

HI Rafael,


On 7/16/2018 2:21 PM, Rafael J. Wysocki wrote:
> On Thu, Jul 12, 2018 at 12:57 PM, Vivek Gautam
> <vivek.gautam@codeaurora.org> wrote:
>> Hi,
>>
>>
>> On Wed, Jul 11, 2018 at 6:21 PM, Tomasz Figa <tfiga@chromium.org> wrote:
>>> On Wed, Jul 11, 2018 at 8:11 PM Rafael J. Wysocki <rafael@kernel.org> wrote:
>>>> On Wed, Jul 11, 2018 at 12:55 PM, Vivek Gautam
>>>> <vivek.gautam@codeaurora.org> wrote:
>>>>> Hi Rafael,
>>>>>
>>>>>
>>>>> On Wed, Jul 11, 2018 at 3:20 PM, Rafael J. Wysocki <rjw@rjwysocki.net> wrote:
>>>>>> On Sunday, July 8, 2018 7:34:10 PM CEST Vivek Gautam wrote:
>>>>>>> From: Sricharan R <sricharan@codeaurora.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@codeaurora.org>
>>>>>>> Signed-off-by: Archit Taneja <architt@codeaurora.org>
>>>>>>> [vivek: Clock rework to request bulk of clocks]
>>>>>>> Signed-off-by: Vivek Gautam <vivek.gautam@codeaurora.org>
>>>>>>> Reviewed-by: Tomasz Figa <tfiga@chromium.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.
>> My bad, apologies. You are right, we were discussing if we need any additional
>> handling of power for arm_smmu_device_reset() in arm_smmu_pm_resume().
>>
>>> 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.
>> Will add the following suspend callback (same as arm_smmu_runtime_suspend):
>>
>>   static int __maybe_unused arm_smmu_pm_suspend(struct device *dev)
>>   {
>>           struct arm_smmu_device *smmu = dev_get_drvdata(dev);
>>
>>           clk_bulk_disable(smmu->num_clks, smmu->clks);
>>
>>           return 0;
>>   }
> I think you also need to check if the clock has already been disabled
> by runtime PM.  Otherwise you may end up disabling it twice in a row.

Should I rather call a pm_runtime_put() in suspend callback? Or an 
expanded form
something similar to:
https://elixir.bootlin.com/linux/v4.18-rc5/source/drivers/slimbus/qcom-ctrl.c#L695


Best regards
Vivek