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

[Rafael J. Wysocki]

On Thu, Jul 12, 2018 at 12:57 PM, Vivek Gautam
<vivek.gautam@xxxxxxxxxxxxxx> wrote:
> Hi,
>
>
> On Wed, Jul 11, 2018 at 6:21 PM, Tomasz Figa <tfiga@xxxxxxxxxxxx> wrote:
>> On Wed, Jul 11, 2018 at 8:11 PM Rafael J. Wysocki <rafael@xxxxxxxxxx> wrote:
>>>
>>> On Wed, Jul 11, 2018 at 12:55 PM, Vivek Gautam
>>> <vivek.gautam@xxxxxxxxxxxxxx> wrote:
>>> > Hi Rafael,
>>> >
>>> >
>>> > On Wed, Jul 11, 2018 at 3:20 PM, Rafael J. Wysocki <rjw@xxxxxxxxxxxxx> wrote:
>>> >> On Sunday, July 8, 2018 7:34:10 PM CEST Vivek Gautam wrote:
>>> >>> From: Sricharan R <sricharan@xxxxxxxxxxxxxx>
>>> >>>
>>> >>> 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@xxxxxxxxxxxxxx>
>>> >>> Signed-off-by: Archit Taneja <architt@xxxxxxxxxxxxxx>
>>> >>> [vivek: Clock rework to request bulk of clocks]
>>> >>> Signed-off-by: Vivek Gautam <vivek.gautam@xxxxxxxxxxxxxx>
>>> >>> Reviewed-by: Tomasz Figa <tfiga@xxxxxxxxxxxx>
>>> >>> ---
>>> >>>
>>> >>>  - 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.