Re: [PATCH v9 28/32] misc: fastrpc: fix common struct sg_table related issues
From: Robin Murphy <robin.murphy@arm.com>
Date: 2020-09-01 20:14:14
Also in:
dri-devel, linux-iommu, lkml
On 2020-08-26 07:33, 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.Reviewed-by: Robin Murphy <robin.murphy@arm.com>
quoted hunk ↗ jump to hunk
Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com> --- 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 7939c55daceb..9d6867749316 100644 --- a/drivers/misc/fastrpc.c +++ b/drivers/misc/fastrpc.c@@ -518,7 +518,7 @@ fastrpc_map_dma_buf(struct dma_buf_attachment *attachment, table = &a->sgt; - if (!dma_map_sg(attachment->dev, table->sgl, table->nents, dir)) + if (!dma_map_sgtable(attachment->dev, table, dir, 0)) 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, 0); } static void fastrpc_release(struct dma_buf *dmabuf)
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