drm/panfrost: Remove unnecessary mmu->lock mutex

There's no need to serialize io-pgtable calls and the as_lock is
sufficient to serialize flush operations, so we can remove the per
page table lock.

Fixes: 7282f764 ("drm/panfrost: Implement per FD address spaces")
Suggested-by: Robin Murphy <robin.murphy@arm.com>
Cc: Tomeu Vizoso <tomeu.vizoso@collabora.com>
Cc: David Airlie <airlied@linux.ie>
Cc: Daniel Vetter <daniel@ffwll.ch>
Signed-off-by: Rob Herring <robh@kernel.org>
Acked-by: Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>
Reviewed-by: Robin Murphy <robin.murphy@arm.com>
Reviewed-by: Steven Price <steven.price@arm.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190826223317.28509-4-robh@kernel.org

drivers/gpu/drm/panfrost/panfrost_device.h

@@ -104,7 +104,6 @@ struct panfrost_device {
 struct panfrost_mmu {
 	struct io_pgtable_cfg pgtbl_cfg;
 	struct io_pgtable_ops *pgtbl_ops;
-	struct mutex lock;
 	int as;
 	atomic_t as_count;
 	struct list_head list;

drivers/gpu/drm/panfrost/panfrost_mmu.c

@@ -228,8 +228,6 @@ static int mmu_map_sg(struct panfrost_device *pfdev, struct panfrost_mmu *mmu,
 	struct io_pgtable_ops *ops = mmu->pgtbl_ops;
 	u64 start_iova = iova;
 
-	mutex_lock(&mmu->lock);
-
 	for_each_sg(sgt->sgl, sgl, sgt->nents, count) {
 		unsigned long paddr = sg_dma_address(sgl);
 		size_t len = sg_dma_len(sgl);
@@ -249,8 +247,6 @@ 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);
 
-	mutex_unlock(&mmu->lock);
-
 	return 0;
 }
 
@@ -304,8 +300,6 @@ void panfrost_mmu_unmap(struct panfrost_gem_object *bo)
 	if (ret < 0)
 		return;
 
-	mutex_lock(&bo->mmu->lock);
-
 	while (unmapped_len < len) {
 		size_t unmapped_page;
 		size_t pgsize = get_pgsize(iova, len - unmapped_len);
@@ -321,8 +315,6 @@ void panfrost_mmu_unmap(struct panfrost_gem_object *bo)
 	mmu_hw_do_operation(pfdev, bo->mmu, bo->node.start << PAGE_SHIFT,
 			    bo->node.size << PAGE_SHIFT, AS_COMMAND_FLUSH_PT);
 
-	mutex_unlock(&bo->mmu->lock);
-
 	pm_runtime_mark_last_busy(pfdev->dev);
 	pm_runtime_put_autosuspend(pfdev->dev);
 	bo->is_mapped = false;
@@ -356,7 +348,6 @@ int panfrost_mmu_pgtable_alloc(struct panfrost_file_priv *priv)
 	struct panfrost_mmu *mmu = &priv->mmu;
 	struct panfrost_device *pfdev = priv->pfdev;
 
-	mutex_init(&mmu->lock);
 	INIT_LIST_HEAD(&mmu->list);
 	mmu->as = -1;