Re: [PATCH] iommu/arm-smmu: Add clk_bulk_{prepare/unprepare} to system pm callbacks

[Robin Murphy <robin.murphy@arm.com>]

On 2021-07-27 11:25, Robin Murphy wrote:
> On 2021-07-27 10:33, Sai Prakash Ranjan wrote:
>> Some clocks for SMMU can have parent as XO such as gpu_cc_hub_cx_int_clk
>> of GPU SMMU in QTI SC7280 SoC and in order to enter deep sleep states in
>> such cases, we would need to drop the XO clock vote in unprepare call and
>> this unprepare callback for XO is in RPMh (Resource Power 
>> Manager-Hardened)
>> clock driver which controls RPMh managed clock resources for new QTI SoCs
>> and is a blocking call.
>>
>> Given we cannot have a sleeping calls such as clk_bulk_prepare() and
>> clk_bulk_unprepare() in arm-smmu runtime pm callbacks since the iommu
>> operations like map and unmap can be in atomic context and are in fast
>> path, add this prepare and unprepare call to drop the XO vote only for
>> system pm callbacks since it is not a fast path and we expect the system
>> to enter deep sleep states with system pm as opposed to runtime pm.
>>
>> This is a similar sequence of clock requests (prepare,enable and
>> disable,unprepare) in arm-smmu probe and remove.
> 
> Nope. We call arm_smmu_rpm_get(), which may resume the device, from 
> atomic contexts. clk_prepare() may sleep. This doesn't work.

Urgh, or maybe I skimmed the commit message too lightly *and* managed to 
totally misread the patch, sorry :(

I'll wake up some more and try again later...

Robin.

>> Signed-off-by: Sai Prakash Ranjan <saiprakash.ranjan@codeaurora.org>
>> Co-developed-by: Rajendra Nayak <rnayak@codeaurora.org>
>> Signed-off-by: Rajendra Nayak <rnayak@codeaurora.org>
>> ---
>>   drivers/iommu/arm/arm-smmu/arm-smmu.c | 20 ++++++++++++++++++--
>>   1 file changed, 18 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/iommu/arm/arm-smmu/arm-smmu.c 
>> b/drivers/iommu/arm/arm-smmu/arm-smmu.c
>> index d3c6f54110a5..9561ba4c5d39 100644
>> --- a/drivers/iommu/arm/arm-smmu/arm-smmu.c
>> +++ b/drivers/iommu/arm/arm-smmu/arm-smmu.c
>> @@ -2277,6 +2277,13 @@ static int __maybe_unused 
>> arm_smmu_runtime_suspend(struct device *dev)
>>   static int __maybe_unused arm_smmu_pm_resume(struct device *dev)
>>   {
>> +    int ret;
>> +    struct arm_smmu_device *smmu = dev_get_drvdata(dev);
>> +
>> +    ret = clk_bulk_prepare(smmu->num_clks, smmu->clks);
>> +    if (ret)
>> +        return ret;
>> +
>>       if (pm_runtime_suspended(dev))
>>           return 0;
>> @@ -2285,10 +2292,19 @@ static int __maybe_unused 
>> arm_smmu_pm_resume(struct device *dev)
>>   static int __maybe_unused arm_smmu_pm_suspend(struct device *dev)
>>   {
>> +    int ret = 0;
>> +    struct arm_smmu_device *smmu = dev_get_drvdata(dev);
>> +
>>       if (pm_runtime_suspended(dev))
>> -        return 0;
>> +        goto clk_unprepare;
>> -    return arm_smmu_runtime_suspend(dev);
>> +    ret = arm_smmu_runtime_suspend(dev);
>> +    if (ret)
>> +        return ret;
>> +
>> +clk_unprepare:
>> +    clk_bulk_unprepare(smmu->num_clks, smmu->clks);
>> +    return ret;
>>   }
>>   static const struct dev_pm_ops arm_smmu_pm_ops = {
>>
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