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

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Message-ID: <955a3034-f7e7-f8f9-4abd-b65efbfbb404@arm.com>
Date:   Tue, 27 Jul 2021 11:25:50 +0100
From:   Robin Murphy <robin.murphy@....com>
To:     Sai Prakash Ranjan <saiprakash.ranjan@...eaurora.org>,
        Will Deacon <will@...nel.org>, Joerg Roedel <joro@...tes.org>,
        Rajendra Nayak <rnayak@...eaurora.org>,
        Taniya Das <tdas@...eaurora.org>,
        srimuc <srimuc@...eaurora.org>
Cc:     linux-arm-msm@...r.kernel.org, iommu@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH] iommu/arm-smmu: Add clk_bulk_{prepare/unprepare} to
 system pm callbacks

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@...eaurora.org>
> Co-developed-by: Rajendra Nayak <rnayak@...eaurora.org>
> Signed-off-by: Rajendra Nayak <rnayak@...eaurora.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 = {
>