On 2020-08-26 07:32, Marek Szyprowski wrote:
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
drivers/gpu/drm/drm_cache.c | 2 +- drivers/gpu/drm/drm_gem_shmem_helper.c | 14 +++++++++----- drivers/gpu/drm/drm_prime.c | 11 ++++++----- 3 files changed, 16 insertions(+), 11 deletions(-)
diff --git a/drivers/gpu/drm/drm_cache.c b/drivers/gpu/drm/drm_cache.c index 03e01b000f7a..0fe3c496002a 100644 --- 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));diff --git a/drivers/gpu/drm/drm_gem_shmem_helper.c b/drivers/gpu/drm/drm_gem_shmem_helper.c index 4b7cfbac4daa..47d8211221f2 100644 --- 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);
Should this be a separate patch to add the missing error handling to the existing code first?
Otherwise the rest of the mechanical conversion looks straightforward enough, and I'm not the separation-of-concerns police (for this subsystem, at least), so either way,
Reviewed-by: Robin Murphy robin.murphy@arm.com
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 5d181bf60a44..c45b0cc6e31d 100644 --- 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); }