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

[Will Deacon <will@kernel.org>]

Hi Rob,

On Mon, Oct 07, 2019 at 01:49:06PM -0700, 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.

Please can you reword the subject to be a bit more useful? The commit
message is great, but the subject is a bit like "fix bug in code" to me.

> 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);

Please can you put a comment here explaining what this is doing? An abridged
version of the commit message is fine.

> +	pm_runtime_set_autosuspend_delay(smmu->dev, 20);
> +	pm_runtime_use_autosuspend(smmu->dev);

Cheers,

Will