[PATCH v3 4/8] drm/panfrost: Rework page table flushing and runtime PM interaction

[Robin Murphy]

On 26/08/2019 23:33, Rob Herring wrote:
> There is no point in resuming the h/w just to do flush operations and
> doing so takes several locks which cause lockdep issues with the shrinker.
> Rework the flush operations to only happen when the h/w is already awake.
> This avoids taking any locks associated with resuming which trigger
> lockdep warnings.

Dunno if it's worth explicitly commenting that this is because resume 
already implies a full flush, but regardless,

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

> Fixes: 013b65101315 ("drm/panfrost: Add madvise and shrinker support")
> Cc: Tomeu Vizoso <tomeu.vizoso at collabora.com>
> Cc: Steven Price <steven.price at arm.com>
> Cc: Alyssa Rosenzweig <alyssa.rosenzweig at collabora.com>
> Cc: David Airlie <airlied at linux.ie>
> Cc: Daniel Vetter <daniel at ffwll.ch>
> Signed-off-by: Rob Herring <robh at kernel.org>
> ---
> v3:
>   - Use pm_runtime_get_noresume() and pm_runtime_active() instead of
>     pm_runtime_get_if_not_used(). The problem is pm_runtime_get_if_not_used()
>     returns 0 (no get) if in the period between the last put()
>     and before the autosuspend timeout when the h/w is still active.
> 
>   drivers/gpu/drm/panfrost/panfrost_mmu.c | 38 ++++++++++++-------------
>   1 file changed, 18 insertions(+), 20 deletions(-)
> 
> diff --git a/drivers/gpu/drm/panfrost/panfrost_mmu.c b/drivers/gpu/drm/panfrost/panfrost_mmu.c
> index 3a8bcfa7e7b6..2204e60f7808 100644
> --- a/drivers/gpu/drm/panfrost/panfrost_mmu.c
> +++ b/drivers/gpu/drm/panfrost/panfrost_mmu.c
> @@ -220,6 +220,22 @@ static size_t get_pgsize(u64 addr, size_t size)
>   	return SZ_2M;
>   }
> 
> +void panfrost_mmu_flush_range(struct panfrost_device *pfdev,
> +			      struct panfrost_mmu *mmu,
> +			      u64 iova, size_t size)
> +{
> +	if (mmu->as < 0)
> +		return;
> +
> +	pm_runtime_get_noresume(pfdev->dev);
> +
> +	/* Flush the PTs only if we're already awake */
> +	if (pm_runtime_active(pfdev->dev))
> +		mmu_hw_do_operation(pfdev, mmu, iova, size, AS_COMMAND_FLUSH_PT);
> +
> +	pm_runtime_put_sync_autosuspend(pfdev->dev);
> +}
> +
>   static int mmu_map_sg(struct panfrost_device *pfdev, struct panfrost_mmu *mmu,
>   		      u64 iova, int prot, struct sg_table *sgt)
>   {
> @@ -244,8 +260,7 @@ static int mmu_map_sg(struct panfrost_device *pfdev, struct panfrost_mmu *mmu,
>   		}
>   	}
> 
> -	mmu_hw_do_operation(pfdev, mmu, start_iova, iova - start_iova,
> -			    AS_COMMAND_FLUSH_PT);
> +	panfrost_mmu_flush_range(pfdev, mmu, start_iova, iova - start_iova);
> 
>   	return 0;
>   }
> @@ -255,7 +270,6 @@ int panfrost_mmu_map(struct panfrost_gem_object *bo)
>   	struct drm_gem_object *obj = &bo->base.base;
>   	struct panfrost_device *pfdev = to_panfrost_device(obj->dev);
>   	struct sg_table *sgt;
> -	int ret;
>   	int prot = IOMMU_READ | IOMMU_WRITE;
> 
>   	if (WARN_ON(bo->is_mapped))
> @@ -268,14 +282,7 @@ int panfrost_mmu_map(struct panfrost_gem_object *bo)
>   	if (WARN_ON(IS_ERR(sgt)))
>   		return PTR_ERR(sgt);
> 
> -	ret = pm_runtime_get_sync(pfdev->dev);
> -	if (ret < 0)
> -		return ret;
> -
>   	mmu_map_sg(pfdev, bo->mmu, bo->node.start << PAGE_SHIFT, prot, sgt);
> -
> -	pm_runtime_mark_last_busy(pfdev->dev);
> -	pm_runtime_put_autosuspend(pfdev->dev);
>   	bo->is_mapped = true;
> 
>   	return 0;
> @@ -289,17 +296,12 @@ void panfrost_mmu_unmap(struct panfrost_gem_object *bo)
>   	u64 iova = bo->node.start << PAGE_SHIFT;
>   	size_t len = bo->node.size << PAGE_SHIFT;
>   	size_t unmapped_len = 0;
> -	int ret;
> 
>   	if (WARN_ON(!bo->is_mapped))
>   		return;
> 
>   	dev_dbg(pfdev->dev, "unmap: as=%d, iova=%llx, len=%zx", bo->mmu->as, iova, len);
> 
> -	ret = pm_runtime_get_sync(pfdev->dev);
> -	if (ret < 0)
> -		return;
> -
>   	while (unmapped_len < len) {
>   		size_t unmapped_page;
>   		size_t pgsize = get_pgsize(iova, len - unmapped_len);
> @@ -312,11 +314,7 @@ void panfrost_mmu_unmap(struct panfrost_gem_object *bo)
>   		unmapped_len += pgsize;
>   	}
> 
> -	mmu_hw_do_operation(pfdev, bo->mmu, bo->node.start << PAGE_SHIFT,
> -			    bo->node.size << PAGE_SHIFT, AS_COMMAND_FLUSH_PT);
> -
> -	pm_runtime_mark_last_busy(pfdev->dev);
> -	pm_runtime_put_autosuspend(pfdev->dev);
> +	panfrost_mmu_flush_range(pfdev, bo->mmu, bo->node.start << PAGE_SHIFT, len);
>   	bo->is_mapped = false;
>   }
> 
> --
> 2.20.1
>