drm: core: 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>
Reviewed-by: Andrzej Hajda <a.hajda@samsung.com>
Reviewed-by: Robin Murphy <robin.murphy@arm.com>

diff --git a/drivers/gpu/drm/drm_cache.c b/drivers/gpu/drm/drm_cache.c
index 03e01b0..0fe3c49 100644 (file)
--- a/drivers/gpu/drm/drm_cache.c
+++ b/drivers/gpu/drm/drm_cache.c
@@ -127,7 +127,7 @@ drm_clflush_sg(struct sg_table *st)
                struct sg_page_iter sg_iter;
 
                mb(); /*CLFLUSH is ordered only by using memory barriers*/
-               for_each_sg_page(st->sgl, &sg_iter, st->nents, 0)
+               for_each_sgtable_page(st, &sg_iter, 0)
                        drm_clflush_page(sg_page_iter_page(&sg_iter));
                mb(); /*Make sure that all cache line entry is flushed*/
 

diff --git a/drivers/gpu/drm/drm_gem_shmem_helper.c b/drivers/gpu/drm/drm_gem_shmem_helper.c
index 4b7cfba..47d8211 100644 (file)
--- a/drivers/gpu/drm/drm_gem_shmem_helper.c
+++ b/drivers/gpu/drm/drm_gem_shmem_helper.c
@@ -126,8 +126,8 @@ void drm_gem_shmem_free_object(struct drm_gem_object *obj)
                drm_prime_gem_destroy(obj, shmem->sgt);
        } else {
                if (shmem->sgt) {
-                       dma_unmap_sg(obj->dev->dev, shmem->sgt->sgl,
-                                    shmem->sgt->nents, DMA_BIDIRECTIONAL);
+                       dma_unmap_sgtable(obj->dev->dev, shmem->sgt,
+                                         DMA_BIDIRECTIONAL, 0);
                        sg_free_table(shmem->sgt);
                        kfree(shmem->sgt);
                }
@@ -424,8 +424,7 @@ void drm_gem_shmem_purge_locked(struct drm_gem_object *obj)
 
        WARN_ON(!drm_gem_shmem_is_purgeable(shmem));
 
-       dma_unmap_sg(obj->dev->dev, shmem->sgt->sgl,
-                    shmem->sgt->nents, DMA_BIDIRECTIONAL);
+       dma_unmap_sgtable(obj->dev->dev, shmem->sgt, DMA_BIDIRECTIONAL, 0);
        sg_free_table(shmem->sgt);
        kfree(shmem->sgt);
        shmem->sgt = NULL;
@@ -697,12 +696,17 @@ struct sg_table *drm_gem_shmem_get_pages_sgt(struct drm_gem_object *obj)
                goto err_put_pages;
        }
        /* Map the pages for use by the h/w. */
-       dma_map_sg(obj->dev->dev, sgt->sgl, sgt->nents, DMA_BIDIRECTIONAL);
+       ret = dma_map_sgtable(obj->dev->dev, sgt, DMA_BIDIRECTIONAL, 0);
+       if (ret)
+               goto err_free_sgt;
 
        shmem->sgt = sgt;
 
        return sgt;
 
+err_free_sgt:
+       sg_free_table(sgt);
+       kfree(sgt);
 err_put_pages:
        drm_gem_shmem_put_pages(shmem);
        return ERR_PTR(ret);

diff --git a/drivers/gpu/drm/drm_prime.c b/drivers/gpu/drm/drm_prime.c
index c5e796d..b8c7f06 100644 (file)
--- a/drivers/gpu/drm/drm_prime.c
+++ b/drivers/gpu/drm/drm_prime.c
@@ -617,6 +617,7 @@ struct sg_table *drm_gem_map_dma_buf(struct dma_buf_attachment *attach,
 {
        struct drm_gem_object *obj = attach->dmabuf->priv;
        struct sg_table *sgt;
+       int ret;
 
        if (WARN_ON(dir == DMA_NONE))
                return ERR_PTR(-EINVAL);
@@ -626,11 +627,12 @@ struct sg_table *drm_gem_map_dma_buf(struct dma_buf_attachment *attach,
        else
                sgt = obj->dev->driver->gem_prime_get_sg_table(obj);
 
-       if (!dma_map_sg_attrs(attach->dev, sgt->sgl, sgt->nents, dir,
-                             DMA_ATTR_SKIP_CPU_SYNC)) {
+       ret = dma_map_sgtable(attach->dev, sgt, dir,
+                             DMA_ATTR_SKIP_CPU_SYNC);
+       if (ret) {
                sg_free_table(sgt);
                kfree(sgt);
-               sgt = ERR_PTR(-ENOMEM);
+               sgt = ERR_PTR(ret);
        }
 
        return sgt;
@@ -652,8 +654,7 @@ void drm_gem_unmap_dma_buf(struct dma_buf_attachment *attach,
        if (!sgt)
                return;
 
-       dma_unmap_sg_attrs(attach->dev, sgt->sgl, sgt->nents, dir,
-                          DMA_ATTR_SKIP_CPU_SYNC);
+       dma_unmap_sgtable(attach->dev, sgt, dir, DMA_ATTR_SKIP_CPU_SYNC);
        sg_free_table(sgt);
        kfree(sgt);
 }