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

Sai Prakash Ranjan
2021-07-27T10:35:38Z

Hi Robin,

On 2021-07-27 16:03, Robin Murphy wrote:
> 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...
>

No worries, we took our time looking through that many times before
posting this :)

Thanks,
Sai

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