drm: virtio: fix common struct sg_table related issues

The Documentation/DMA-API-HOWTO.txt states that the dma_map_sg() function
returns the number of the created entries in the DMA address space.
However the subsequent calls to the dma_sync_sg_for_{device,cpu}() and
dma_unmap_sg must be called with the original number of the entries
passed to the dma_map_sg().

struct sg_table is a common structure used for describing a non-contiguous
memory buffer, used commonly in the DRM and graphics subsystems. It
consists of a scatterlist with memory pages and DMA addresses (sgl entry),
as well as the number of scatterlist entries: CPU pages (orig_nents entry)
and DMA mapped pages (nents entry).

It turned out that it was a common mistake to misuse nents and orig_nents
entries, calling DMA-mapping functions with a wrong number of entries or
ignoring the number of mapped entries returned by the dma_map_sg()
function.

To avoid such issues, lets use a common dma-mapping wrappers operating
directly on the struct sg_table objects and use scatterlist page
iterators where possible. This, almost always, hides references to the
nents and orig_nents entries, making the code robust, easier to follow
and copy/paste safe.

Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Acked-by: Gerd Hoffmann <kraxel@redhat.com>

diff --git a/drivers/gpu/drm/virtio/virtgpu_object.c b/drivers/gpu/drm/virtio/virtgpu_object.c
index 2cdd3cd9ce75fc44599310212aeec301fd68ee5f..5419b7f41af08469ce44a6126db2625122f8fc8b 100644 (file)
--- a/drivers/gpu/drm/virtio/virtgpu_object.c
+++ b/drivers/gpu/drm/virtio/virtgpu_object.c
@@ -72,9 +72,8 @@ void virtio_gpu_cleanup_object(struct virtio_gpu_object *bo)
 
                if (shmem->pages) {
                        if (shmem->mapped) {
-                               dma_unmap_sg(vgdev->vdev->dev.parent,
-                                            shmem->pages->sgl, shmem->mapped,
-                                            DMA_TO_DEVICE);
+                               dma_unmap_sgtable(vgdev->vdev->dev.parent,
+                                            shmem->pages, DMA_TO_DEVICE, 0);
                                shmem->mapped = 0;
                        }
 
@@ -157,13 +156,13 @@ static int virtio_gpu_object_shmem_init(struct virtio_gpu_device *vgdev,
        }
 
        if (use_dma_api) {
-               shmem->mapped = dma_map_sg(vgdev->vdev->dev.parent,
-                                          shmem->pages->sgl,
-                                          shmem->pages->nents,
-                                          DMA_TO_DEVICE);
-               *nents = shmem->mapped;
+               ret = dma_map_sgtable(vgdev->vdev->dev.parent,
+                                     shmem->pages, DMA_TO_DEVICE, 0);
+               if (ret)
+                       return ret;
+               *nents = shmem->mapped = shmem->pages->nents;
        } else {
-               *nents = shmem->pages->nents;
+               *nents = shmem->pages->orig_nents;
        }
 
        *ents = kmalloc_array(*nents, sizeof(struct virtio_gpu_mem_entry),
@@ -173,13 +172,20 @@ static int virtio_gpu_object_shmem_init(struct virtio_gpu_device *vgdev,
                return -ENOMEM;
        }
 
-       for_each_sg(shmem->pages->sgl, sg, *nents, si) {
-               (*ents)[si].addr = cpu_to_le64(use_dma_api
-                                              ? sg_dma_address(sg)
-                                              : sg_phys(sg));
-               (*ents)[si].length = cpu_to_le32(sg->length);
-               (*ents)[si].padding = 0;
+       if (use_dma_api) {
+               for_each_sgtable_dma_sg(shmem->pages, sg, si) {
+                       (*ents)[si].addr = cpu_to_le64(sg_dma_address(sg));
+                       (*ents)[si].length = cpu_to_le32(sg_dma_len(sg));
+                       (*ents)[si].padding = 0;
+               }
+       } else {
+               for_each_sgtable_sg(shmem->pages, sg, si) {
+                       (*ents)[si].addr = cpu_to_le64(sg_phys(sg));
+                       (*ents)[si].length = cpu_to_le32(sg->length);
+                       (*ents)[si].padding = 0;
+               }
        }
+
        return 0;
 }
 

diff --git a/drivers/gpu/drm/virtio/virtgpu_vq.c b/drivers/gpu/drm/virtio/virtgpu_vq.c
index 53af60d484a4489bc8588be680513e8721cc1601..7947b1047bd076e97f8802c02ca3b98b987a5498 100644 (file)
--- a/drivers/gpu/drm/virtio/virtgpu_vq.c
+++ b/drivers/gpu/drm/virtio/virtgpu_vq.c
@@ -302,7 +302,7 @@ static struct sg_table *vmalloc_to_sgt(char *data, uint32_t size, int *sg_ents)
                return NULL;
        }
 
-       for_each_sg(sgt->sgl, sg, *sg_ents, i) {
+       for_each_sgtable_sg(sgt, sg, i) {
                pg = vmalloc_to_page(data);
                if (!pg) {
                        sg_free_table(sgt);
@@ -603,9 +603,8 @@ void virtio_gpu_cmd_transfer_to_host_2d(struct virtio_gpu_device *vgdev,
        struct virtio_gpu_object_shmem *shmem = to_virtio_gpu_shmem(bo);
 
        if (use_dma_api)
-               dma_sync_sg_for_device(vgdev->vdev->dev.parent,
-                                      shmem->pages->sgl, shmem->pages->nents,
-                                      DMA_TO_DEVICE);
+               dma_sync_sgtable_for_device(vgdev->vdev->dev.parent,
+                                           shmem->pages, DMA_TO_DEVICE);
 
        cmd_p = virtio_gpu_alloc_cmd(vgdev, &vbuf, sizeof(*cmd_p));
        memset(cmd_p, 0, sizeof(*cmd_p));
@@ -1019,9 +1018,8 @@ void virtio_gpu_cmd_transfer_to_host_3d(struct virtio_gpu_device *vgdev,
        struct virtio_gpu_object_shmem *shmem = to_virtio_gpu_shmem(bo);
 
        if (use_dma_api)
-               dma_sync_sg_for_device(vgdev->vdev->dev.parent,
-                                      shmem->pages->sgl, shmem->pages->nents,
-                                      DMA_TO_DEVICE);
+               dma_sync_sgtable_for_device(vgdev->vdev->dev.parent,
+                                           shmem->pages, DMA_TO_DEVICE);
 
        cmd_p = virtio_gpu_alloc_cmd(vgdev, &vbuf, sizeof(*cmd_p));
        memset(cmd_p, 0, sizeof(*cmd_p));