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

[Will Deacon]

On Tue, Jul 27, 2021 at 03:03:22PM +0530, 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.
> 
> Signed-off-by: Sai Prakash Ranjan <saiprakash.ranjan@xxxxxxxxxxxxxx>
> Co-developed-by: Rajendra Nayak <rnayak@xxxxxxxxxxxxxx>
> Signed-off-by: Rajendra Nayak <rnayak@xxxxxxxxxxxxxx>
> ---
>  drivers/iommu/arm/arm-smmu/arm-smmu.c | 20 ++++++++++++++++++--
>  1 file changed, 18 insertions(+), 2 deletions(-)

[+Rob]

How does this work with that funny GPU which writes to the SMMU registers
directly? Does the SMMU need to remain independently clocked for that to
work or is it all in the same clock domain?

> 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;

If we subsequently fail to enable the clks in arm_smmu_runtime_resume()
should we unprepare them again?

Will

> @@ -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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