| Message ID | 20200513133245.6408-29-m.szyprowski@samsung.com (mailing list archive) |
|---|---|
| State | New |
| Delegated to: | Kieran Bingham |
| Headers | show |
| Series | None | expand |
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@samsung.com> This is a very nice simplification, I've always foudn the dma_map_sg API cumbersome to use. Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com> 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@samsung.com/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); >
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);
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@samsung.com> --- 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@samsung.com/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(-)