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From:   "=?UTF-8?q?Christian=20K=C3=B6nig?=" 
        <ckoenig.leichtzumerken@gmail.com>
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Subject: [PATCH 6/6] drm/prime: document that use the page array is deprecated v2
Date:   Fri,  9 Oct 2020 17:03:42 +0200
Message-Id: <20201009150342.1979-6-christian.koenig@amd.com>
In-Reply-To: <20201009150342.1979-1-christian.koenig@amd.com>
References: <20201009150342.1979-1-christian.koenig@amd.com>
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Precedence: bulk

We have reoccurring requests on this so better document that
this approach doesn't work and dma_buf_mmap() needs to be used instead.

v2: split it into two functions

Signed-off-by: Christian König <christian.koenig@amd.com>
---
 drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c     |  9 ++-
 drivers/gpu/drm/drm_prime.c                 | 67 +++++++++++++++------
 drivers/gpu/drm/etnaviv/etnaviv_gem_prime.c |  3 +-
 drivers/gpu/drm/msm/msm_gem.c               |  2 +-
 drivers/gpu/drm/nouveau/nouveau_bo.c        |  5 +-
 drivers/gpu/drm/radeon/radeon_ttm.c         |  9 ++-
 drivers/gpu/drm/vgem/vgem_drv.c             |  3 +-
 drivers/gpu/drm/vkms/vkms_gem.c             |  2 +-
 drivers/gpu/drm/xen/xen_drm_front_gem.c     |  4 +-
 include/drm/drm_prime.h                     |  7 ++-
 10 files changed, 69 insertions(+), 42 deletions(-)

diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
index ac463e706b19..6a65490de391 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
@@ -1011,8 +1011,8 @@ static int amdgpu_ttm_tt_pin_userptr(struct ttm_bo_device *bdev,
 		goto release_sg;
 
 	/* convert SG to linear array of pages and dma addresses */
-	drm_prime_sg_to_page_addr_arrays(ttm->sg, NULL, gtt->ttm.dma_address,
-					 ttm->num_pages);
+	drm_prime_sg_to_dma_addr_array(ttm->sg, gtt->ttm.dma_address,
+				       ttm->num_pages);
 
 	return 0;
 
@@ -1345,9 +1345,8 @@ static int amdgpu_ttm_tt_populate(struct ttm_bo_device *bdev,
 			ttm->sg = sgt;
 		}
 
-		drm_prime_sg_to_page_addr_arrays(ttm->sg, NULL,
-						 gtt->ttm.dma_address,
-						 ttm->num_pages);
+		drm_prime_sg_to_dma_addr_array(ttm->sg, gtt->ttm.dma_address,
+					       ttm->num_pages);
 		ttm_tt_set_populated(ttm);
 		return 0;
 	}
diff --git a/drivers/gpu/drm/drm_prime.c b/drivers/gpu/drm/drm_prime.c
index 4910c446db83..8b750c074494 100644
--- a/drivers/gpu/drm/drm_prime.c
+++ b/drivers/gpu/drm/drm_prime.c
@@ -954,27 +954,25 @@ struct drm_gem_object *drm_gem_prime_import(struct drm_device *dev,
 EXPORT_SYMBOL(drm_gem_prime_import);
 
 /**
- * drm_prime_sg_to_page_addr_arrays - convert an sg table into a page array
+ * drm_prime_sg_to_page_array - convert an sg table into a page array
  * @sgt: scatter-gather table to convert
- * @pages: optional array of page pointers to store the page array in
- * @addrs: optional array to store the dma bus address of each page
- * @max_entries: size of both the passed-in arrays
+ * @pages: array of page pointers to store the pages in
+ * @max_entries: size of the passed-in array
  *
- * Exports an sg table into an array of pages and addresses. This is currently
- * required by the TTM driver in order to do correct fault handling.
+ * Exports an sg table into an array of pages.
  *
- * Drivers can use this in their &drm_driver.gem_prime_import_sg_table
- * implementation.
+ * This function is deprecated and strongly discouraged to be used.
+ * The page array is only useful for page faults and those can corrupt fields
+ * in the struct page if they are not handled by the exporting driver.
  */
-int drm_prime_sg_to_page_addr_arrays(struct sg_table *sgt, struct page **pages,
-				     dma_addr_t *addrs, int max_entries)
+int __deprecated drm_prime_sg_to_page_array(struct sg_table *sgt,
+					    struct page **pages,
+					    int max_entries)
 {
 	unsigned count;
 	struct scatterlist *sg;
 	struct page *page;
 	u32 page_len, page_index;
-	dma_addr_t addr;
-	u32 dma_len, dma_index;
 
 	/*
 	 * Scatterlist elements contains both pages and DMA addresses, but
@@ -984,14 +982,11 @@ int drm_prime_sg_to_page_addr_arrays(struct sg_table *sgt, struct page **pages,
 	 * described by the sg_dma_address(sg).
 	 */
 	page_index = 0;
-	dma_index = 0;
 	for_each_sg(sgt->sgl, sg, sgt->nents, count) {
 		page_len = sg->length;
 		page = sg_page(sg);
-		dma_len = sg_dma_len(sg);
-		addr = sg_dma_address(sg);
 
-		while (pages && page_len > 0) {
+		while (page_len > 0) {
 			if (WARN_ON(page_index >= max_entries))
 				return -1;
 			pages[page_index] = page;
@@ -999,7 +994,43 @@ int drm_prime_sg_to_page_addr_arrays(struct sg_table *sgt, struct page **pages,
 			page_len -= PAGE_SIZE;
 			page_index++;
 		}
-		while (addrs && dma_len > 0) {
+	}
+	return 0;
+}
+EXPORT_SYMBOL(drm_prime_sg_to_page_array);
+
+/**
+ * drm_prime_sg_to_dma_addr_array - convert an sg table into a dma addr array
+ * @sgt: scatter-gather table to convert
+ * @addrs: array to store the dma bus address of each page
+ * @max_entries: size of both the passed-in arrays
+ *
+ * Exports an sg table into an array of addresses.
+ *
+ * Drivers should use this in their &drm_driver.gem_prime_import_sg_table
+ * implementation.
+ */
+int drm_prime_sg_to_dma_addr_array(struct sg_table *sgt, dma_addr_t *addrs,
+				   int max_entries)
+{
+	struct scatterlist *sg;
+	u32 dma_len, dma_index;
+	dma_addr_t addr;
+	unsigned count;
+
+	/*
+	 * Scatterlist elements contains both pages and DMA addresses, but
+	 * one shoud not assume 1:1 relation between them. The sg->length is
+	 * the size of the physical memory chunk described by the sg->page,
+	 * while sg_dma_len(sg) is the size of the DMA (IO virtual) chunk
+	 * described by the sg_dma_address(sg).
+	 */
+	dma_index = 0;
+	for_each_sg(sgt->sgl, sg, sgt->nents, count) {
+		dma_len = sg_dma_len(sg);
+		addr = sg_dma_address(sg);
+
+		while (dma_len > 0) {
 			if (WARN_ON(dma_index >= max_entries))
 				return -1;
 			addrs[dma_index] = addr;
@@ -1010,7 +1041,7 @@ int drm_prime_sg_to_page_addr_arrays(struct sg_table *sgt, struct page **pages,
 	}
 	return 0;
 }
-EXPORT_SYMBOL(drm_prime_sg_to_page_addr_arrays);
+EXPORT_SYMBOL(drm_prime_sg_to_dma_addr_array);
 
 /**
  * drm_prime_gem_destroy - helper to clean up a PRIME-imported GEM object
diff --git a/drivers/gpu/drm/etnaviv/etnaviv_gem_prime.c b/drivers/gpu/drm/etnaviv/etnaviv_gem_prime.c
index 135fbff6fecf..8c04b8e8054c 100644
--- a/drivers/gpu/drm/etnaviv/etnaviv_gem_prime.c
+++ b/drivers/gpu/drm/etnaviv/etnaviv_gem_prime.c
@@ -133,8 +133,7 @@ struct drm_gem_object *etnaviv_gem_prime_import_sg_table(struct drm_device *dev,
 		goto fail;
 	}
 
-	ret = drm_prime_sg_to_page_addr_arrays(sgt, etnaviv_obj->pages,
-					       NULL, npages);
+	ret = drm_prime_sg_to_page_array(sgt, etnaviv_obj->pages, npages);
 	if (ret)
 		goto fail;
 
diff --git a/drivers/gpu/drm/msm/msm_gem.c b/drivers/gpu/drm/msm/msm_gem.c
index a71f42870d5e..616b87641740 100644
--- a/drivers/gpu/drm/msm/msm_gem.c
+++ b/drivers/gpu/drm/msm/msm_gem.c
@@ -1174,7 +1174,7 @@ struct drm_gem_object *msm_gem_import(struct drm_device *dev,
 		goto fail;
 	}
 
-	ret = drm_prime_sg_to_page_addr_arrays(sgt, msm_obj->pages, NULL, npages);
+	ret = drm_prime_sg_to_page_array(sgt, msm_obj->pages, npages);
 	if (ret) {
 		mutex_unlock(&msm_obj->lock);
 		goto fail;
diff --git a/drivers/gpu/drm/nouveau/nouveau_bo.c b/drivers/gpu/drm/nouveau/nouveau_bo.c
index e378bb491688..835edd74ef59 100644
--- a/drivers/gpu/drm/nouveau/nouveau_bo.c
+++ b/drivers/gpu/drm/nouveau/nouveau_bo.c
@@ -1299,9 +1299,8 @@ nouveau_ttm_tt_populate(struct ttm_bo_device *bdev,
 		return 0;
 
 	if (slave && ttm->sg) {
-		drm_prime_sg_to_page_addr_arrays(ttm->sg, NULL,
-						 ttm_dma->dma_address,
-						 ttm->num_pages);
+		drm_prime_sg_to_dma_addr_array(ttm->sg, ttm_dma->dma_address,
+					       ttm->num_pages);
 		ttm_tt_set_populated(ttm);
 		return 0;
 	}
diff --git a/drivers/gpu/drm/radeon/radeon_ttm.c b/drivers/gpu/drm/radeon/radeon_ttm.c
index 4b92cdbcd29b..7997e4564576 100644
--- a/drivers/gpu/drm/radeon/radeon_ttm.c
+++ b/drivers/gpu/drm/radeon/radeon_ttm.c
@@ -474,8 +474,8 @@ static int radeon_ttm_tt_pin_userptr(struct ttm_bo_device *bdev, struct ttm_tt *
 	if (r)
 		goto release_sg;
 
-	drm_prime_sg_to_page_addr_arrays(ttm->sg, NULL, gtt->ttm.dma_address,
-					 ttm->num_pages);
+	drm_prime_sg_to_dma_addr_array(ttm->sg, gtt->ttm.dma_address,
+				       ttm->num_pages);
 
 	return 0;
 
@@ -642,9 +642,8 @@ static int radeon_ttm_tt_populate(struct ttm_bo_device *bdev,
 	}
 
 	if (slave && ttm->sg) {
-		drm_prime_sg_to_page_addr_arrays(ttm->sg, NULL,
-						 gtt->ttm.dma_address,
-						 ttm->num_pages);
+		drm_prime_sg_to_dma_addr_array(ttm->sg, gtt->ttm.dma_address,
+					       ttm->num_pages);
 		ttm_tt_set_populated(ttm);
 		return 0;
 	}
diff --git a/drivers/gpu/drm/vgem/vgem_drv.c b/drivers/gpu/drm/vgem/vgem_drv.c
index ea0eecae5153..e505e5a291b3 100644
--- a/drivers/gpu/drm/vgem/vgem_drv.c
+++ b/drivers/gpu/drm/vgem/vgem_drv.c
@@ -356,8 +356,7 @@ static struct drm_gem_object *vgem_prime_import_sg_table(struct drm_device *dev,
 	}
 
 	obj->pages_pin_count++; /* perma-pinned */
-	drm_prime_sg_to_page_addr_arrays(obj->table, obj->pages, NULL,
-					npages);
+	drm_prime_sg_to_page_array(obj->table, obj->pages, npages);
 	return &obj->base;
 }
 
diff --git a/drivers/gpu/drm/vkms/vkms_gem.c b/drivers/gpu/drm/vkms/vkms_gem.c
index 19a0e260a4df..a2ff21f47101 100644
--- a/drivers/gpu/drm/vkms/vkms_gem.c
+++ b/drivers/gpu/drm/vkms/vkms_gem.c
@@ -256,6 +256,6 @@ vkms_prime_import_sg_table(struct drm_device *dev,
 		return ERR_PTR(-ENOMEM);
 	}
 
-	drm_prime_sg_to_page_addr_arrays(sg, obj->pages, NULL, npages);
+	drm_prime_sg_to_page_array(sg, obj->pages, npages);
 	return &obj->gem;
 }
diff --git a/drivers/gpu/drm/xen/xen_drm_front_gem.c b/drivers/gpu/drm/xen/xen_drm_front_gem.c
index f3830a0d1808..f4150ddfc5e2 100644
--- a/drivers/gpu/drm/xen/xen_drm_front_gem.c
+++ b/drivers/gpu/drm/xen/xen_drm_front_gem.c
@@ -220,8 +220,8 @@ xen_drm_front_gem_import_sg_table(struct drm_device *dev,
 
 	xen_obj->sgt_imported = sgt;
 
-	ret = drm_prime_sg_to_page_addr_arrays(sgt, xen_obj->pages,
-					       NULL, xen_obj->num_pages);
+	ret = drm_prime_sg_to_page_array(sgt, xen_obj->pages,
+					 xen_obj->num_pages);
 	if (ret < 0)
 		return ERR_PTR(ret);
 
diff --git a/include/drm/drm_prime.h b/include/drm/drm_prime.h
index 093f760cc131..4bda9ab3a3bb 100644
--- a/include/drm/drm_prime.h
+++ b/include/drm/drm_prime.h
@@ -103,8 +103,9 @@ struct drm_gem_object *drm_gem_prime_import(struct drm_device *dev,
 
 void drm_prime_gem_destroy(struct drm_gem_object *obj, struct sg_table *sg);
 
-int drm_prime_sg_to_page_addr_arrays(struct sg_table *sgt, struct page **pages,
-				     dma_addr_t *addrs, int max_pages);
-
+int drm_prime_sg_to_page_array(struct sg_table *sgt, struct page **pages,
+			       int max_pages);
+int drm_prime_sg_to_dma_addr_array(struct sg_table *sgt, dma_addr_t *addrs,
+				   int max_pages);
 
 #endif /* __DRM_PRIME_H__ */
-- 
2.17.1