Re: [PATCH v2] iommu/arm-smmu: fix "hang" when games exit

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

On 2019-10-07 9:49 pm, Rob Clark wrote:
> From: Rob Clark <robdclark@chromium.org>
> 
> When games, browser, or anything using a lot of GPU buffers exits, there
> can be many hundreds or thousands of buffers to unmap and free.  If the
> GPU is otherwise suspended, this can cause arm-smmu to resume/suspend
> for each buffer, resulting 5-10 seconds worth of reprogramming the
> context bank (arm_smmu_write_context_bank()/arm_smmu_write_s2cr()/etc).
> To the user it would appear that the system just locked up.
> 
> A simple solution is to use pm_runtime_put_autosuspend() instead, so we
> don't immediately suspend the SMMU device.

Reviewed-by: Robin Murphy <robin.murphy@arm.com>

> Signed-off-by: Rob Clark <robdclark@chromium.org>
> ---
> v1: original
> v2: unconditionally use autosuspend, rather than deciding based on what
>      consumer does
> 
>   drivers/iommu/arm-smmu.c | 5 ++++-
>   1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/iommu/arm-smmu.c b/drivers/iommu/arm-smmu.c
> index 3f1d55fb43c4..b7b41f5001bc 100644
> --- a/drivers/iommu/arm-smmu.c
> +++ b/drivers/iommu/arm-smmu.c
> @@ -289,7 +289,7 @@ static inline int arm_smmu_rpm_get(struct arm_smmu_device *smmu)
>   static inline void arm_smmu_rpm_put(struct arm_smmu_device *smmu)
>   {
>   	if (pm_runtime_enabled(smmu->dev))
> -		pm_runtime_put(smmu->dev);
> +		pm_runtime_put_autosuspend(smmu->dev);
>   }
>   
>   static struct arm_smmu_domain *to_smmu_domain(struct iommu_domain *dom)
> @@ -1445,6 +1445,9 @@ static int arm_smmu_attach_dev(struct iommu_domain *domain, struct device *dev)
>   	/* Looks ok, so add the device to the domain */
>   	ret = arm_smmu_domain_add_master(smmu_domain, fwspec);
>   
> +	pm_runtime_set_autosuspend_delay(smmu->dev, 20);
> +	pm_runtime_use_autosuspend(smmu->dev);
> +
>   rpm_put:
>   	arm_smmu_rpm_put(smmu);
>   	return ret;
>