Re: [PATCH v13 1/4] iommu/arm-smmu: Add pm_runtime/sleep ops

[Vivek Gautam]

On Wed, Jul 25, 2018 at 11:46 PM, Vivek Gautam
<vivek.gautam@xxxxxxxxxxxxxx> wrote:
> On Tue, Jul 24, 2018 at 8:51 PM, Robin Murphy <robin.murphy@xxxxxxx> wrote:
>> On 19/07/18 11:15, 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.
>>>
>>> Also, while we enable the runtime pm add a pm sleep suspend
>>> callback that pushes devices to low power state by turning
>>> the clocks off in a system sleep.
>>> Also add corresponding clock enable path in resume callback.
>>>
>>> Signed-off-by: Sricharan R <sricharan@xxxxxxxxxxxxxx>
>>> Signed-off-by: Archit Taneja <architt@xxxxxxxxxxxxxx>
>>> [vivek: rework for clock and pm ops]
>>> Signed-off-by: Vivek Gautam <vivek.gautam@xxxxxxxxxxxxxx>
>>> Reviewed-by: Tomasz Figa <tfiga@xxxxxxxxxxxx>
>>> ---
>>>
>>> Changes since v12:
>>>   - Added pm sleep .suspend callback. This disables the clocks.
>>>   - Added corresponding change to enable clocks in .resume
>>>    pm sleep callback.
>>>
>>>   drivers/iommu/arm-smmu.c | 75
>>> ++++++++++++++++++++++++++++++++++++++++++++++--
>>>   1 file changed, 73 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/drivers/iommu/arm-smmu.c b/drivers/iommu/arm-smmu.c
>>> index c73cfce1ccc0..9138a6fffe04 100644
>>> --- a/drivers/iommu/arm-smmu.c
>>> +++ b/drivers/iommu/arm-smmu.c

[snip]

>>> platform_device *pdev)
>>>         arm_smmu_device_remove(pdev);
>>>   }
>>>   +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);
>>
>>
>> If there's a power domain being automatically switched by genpd then we need
>> a reset here because we may have lost state entirely. Since I remembered the
>> otherwise-useless GPU SMMU on Juno is in a separate power domain, I gave it
>> a poking via sysfs with some debug stuff to dump sCR0 in these callbacks,
>> and the problem is clear:
>>
>> ...
>> [    4.625551] arm-smmu 2b400000.iommu: genpd_runtime_suspend()
>> [    4.631163] arm-smmu 2b400000.iommu: arm_smmu_runtime_suspend: 0x00201936
>> [    4.637897] arm-smmu 2b400000.iommu: suspend latency exceeded, 6733980 ns
>> [   21.566983] arm-smmu 2b400000.iommu: genpd_runtime_resume()
>> [   21.584796] arm-smmu 2b400000.iommu: arm_smmu_runtime_resume: 0x00220101
>> [   21.591452] arm-smmu 2b400000.iommu: resume latency exceeded, 6658020 ns
>> ...
>
> Qualcomm SoCs have retention enabled for SMMU registers so they don't
> lose state.
> ...
> [  256.013367] arm-smmu b40000.arm,smmu: arm_smmu_runtime_suspend
> SCR0 = 0x201e36
> [  256.013367]
> [  256.019160] arm-smmu b40000.arm,smmu: arm_smmu_runtime_resume
> SCR0 = 0x201e36
> [  256.019160]
> [  256.027368] arm-smmu b40000.arm,smmu: arm_smmu_runtime_suspend
> SCR0 = 0x201e36
> [  256.027368]
> [  256.036786] arm-smmu b40000.arm,smmu: arm_smmu_runtime_resume
> SCR0 = 0x201e36
> ...
>
> However after adding arm_smmu_device_reset() in runtime_resume() I observe
> some performance degradation when kill an instance of 'kmscube' and
> start it again.
> The launch time with arm_smmu_device_reset() in runtime_resume() change is
> more.
> Could this be because of frequent TLB invalidation and sync?

Some more information that i gathered.
On Qcom SoCs besides the registers retention, TCU invalidates TLB cache on
a CX power collapse exit, which is the system wide suspend case.
The arm-smmu software is not aware of this CX power collapse /
auto-invalidation.

So wouldn't doing an explicit TLB invalidations during runtime resume be
detrimental to performance?

I have one more doubt here -
We do runtime power cycle around arm_smmu_map/unmap() too.
Now during map/unmap we selectively do TLB maintenance (either
tlb_sync or tlb_add_flush).
But with runtime pm we want to do TLBIALL*. Is that a problem?

Best regards
Vivek

>
> Best regards
> Vivek

[snip]

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