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.szyprow...@samsung.com> --- For more information, see '[PATCH v4 00/38] DRM: fix struct sg_table nents vs. orig_nents misuse' thread: https://lore.kernel.org/dri-devel/20200512085710.14688-1-m.szyprow...@samsung.com/T/ --- drivers/misc/fastrpc.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/drivers/misc/fastrpc.c b/drivers/misc/fastrpc.c index e3e085e..0a3e02aa 100644 --- a/drivers/misc/fastrpc.c +++ b/drivers/misc/fastrpc.c @@ -518,7 +518,7 @@ static struct fastrpc_invoke_ctx *fastrpc_context_alloc( table = &a->sgt; - if (!dma_map_sg(attachment->dev, table->sgl, table->nents, dir)) + if (!dma_map_sgtable(attachment->dev, table, dir)) return ERR_PTR(-ENOMEM); return table; @@ -528,7 +528,7 @@ static void fastrpc_unmap_dma_buf(struct dma_buf_attachment *attach, struct sg_table *table, enum dma_data_direction dir) { - dma_unmap_sg(attach->dev, table->sgl, table->nents, dir); + dma_unmap_sgtable(attach->dev, table, dir); } static void fastrpc_release(struct dma_buf *dmabuf) -- 1.9.1 _______________________________________________ dri-devel mailing list dri-devel@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/dri-devel
