| Message ID | 20200826063316.23486-29-m.szyprowski@samsung.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [v9,01/32] drm: prime: add common helper to check scatterlist contiguity | expand |
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> > 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) >
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)
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> --- drivers/misc/fastrpc.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)