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

Robin Murphy
2021-07-27T10:26:00Z

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.

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 = {
>