Hi Marek,
Thank you for the patch.
On Wed, May 13, 2020 at 03:32:36PM +0200, 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.
>
> dma_map_sgtable() function returns zero or an error code, so adjust the
> return value check for the vsp1_du_map_sg() function.
>
> Signed-off-by: Marek Szyprowski <m.szyprowski@xxxxxxxxxxx>
This is a very nice simplification, I've always foudn the dma_map_sg API
cumbersome to use.
Reviewed-by: Laurent Pinchart <laurent.pinchart@xxxxxxxxxxxxxxxx>
I assume you will get the whole series merged in one go. If I need to
pick the patch up at any point, please let me know. Otherwise I'll wait
until I see it upstream, no reply needed :-)
> ---
> For more information, see '[PATCH v5 00/38] DRM: fix struct sg_table nents
> vs. orig_nents misuse' thread:
> https://lore.kernel.org/linux-iommu/20200513132114.6046-1-m.szyprowski@xxxxxxxxxxx/T/
> ---
> drivers/gpu/drm/rcar-du/rcar_du_vsp.c | 3 +--
> drivers/media/platform/vsp1/vsp1_drm.c | 8 ++++----
> 2 files changed, 5 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/gpu/drm/rcar-du/rcar_du_vsp.c b/drivers/gpu/drm/rcar-du/rcar_du_vsp.c
> index 5e4faf2..2fc1816 100644
> --- a/drivers/gpu/drm/rcar-du/rcar_du_vsp.c
> +++ b/drivers/gpu/drm/rcar-du/rcar_du_vsp.c
> @@ -197,9 +197,8 @@ int rcar_du_vsp_map_fb(struct rcar_du_vsp *vsp, struct drm_framebuffer *fb,
> goto fail;
>
> ret = vsp1_du_map_sg(vsp->vsp, sgt);
> - if (!ret) {
> + if (ret) {
> sg_free_table(sgt);
> - ret = -ENOMEM;
> goto fail;
> }
> }
> diff --git a/drivers/media/platform/vsp1/vsp1_drm.c b/drivers/media/platform/vsp1/vsp1_drm.c
> index a4a45d6..86d5e3f 100644
> --- a/drivers/media/platform/vsp1/vsp1_drm.c
> +++ b/drivers/media/platform/vsp1/vsp1_drm.c
> @@ -912,8 +912,8 @@ int vsp1_du_map_sg(struct device *dev, struct sg_table *sgt)
> * skip cache sync. This will need to be revisited when support for
> * non-coherent buffers will be added to the DU driver.
> */
> - return dma_map_sg_attrs(vsp1->bus_master, sgt->sgl, sgt->nents,
> - DMA_TO_DEVICE, DMA_ATTR_SKIP_CPU_SYNC);
> + return dma_map_sgtable(vsp1->bus_master, sgt, DMA_TO_DEVICE,
> + DMA_ATTR_SKIP_CPU_SYNC);
> }
> EXPORT_SYMBOL_GPL(vsp1_du_map_sg);
>
> @@ -921,8 +921,8 @@ void vsp1_du_unmap_sg(struct device *dev, struct sg_table *sgt)
> {
> struct vsp1_device *vsp1 = dev_get_drvdata(dev);
>
> - dma_unmap_sg_attrs(vsp1->bus_master, sgt->sgl, sgt->nents,
> - DMA_TO_DEVICE, DMA_ATTR_SKIP_CPU_SYNC);
> + dma_unmap_sgtable(vsp1->bus_master, sgt, DMA_TO_DEVICE,
> + DMA_ATTR_SKIP_CPU_SYNC);
> }
> EXPORT_SYMBOL_GPL(vsp1_du_unmap_sg);
>
--
Regards,
Laurent Pinchart
