| Message ID | 20200826063316.23486-5-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 07:32, 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. > > Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com> > --- > drivers/gpu/drm/armada/armada_gem.c | 12 ++++++------ > 1 file changed, 6 insertions(+), 6 deletions(-) > > diff --git a/drivers/gpu/drm/armada/armada_gem.c b/drivers/gpu/drm/armada/armada_gem.c > index 8005614d2e6b..bedd8937d8a1 100644 > --- a/drivers/gpu/drm/armada/armada_gem.c > +++ b/drivers/gpu/drm/armada/armada_gem.c > @@ -395,7 +395,7 @@ armada_gem_prime_map_dma_buf(struct dma_buf_attachment *attach, > > mapping = dobj->obj.filp->f_mapping; > > - for_each_sg(sgt->sgl, sg, count, i) { > + for_each_sgtable_sg(sgt, sg, i) { > struct page *page; > > page = shmem_read_mapping_page(mapping, i); > @@ -407,8 +407,8 @@ armada_gem_prime_map_dma_buf(struct dma_buf_attachment *attach, > sg_set_page(sg, page, PAGE_SIZE, 0); > } > > - if (dma_map_sg(attach->dev, sgt->sgl, sgt->nents, dir) == 0) { > - num = sgt->nents; > + if (dma_map_sgtable(attach->dev, sgt, dir, 0)) { > + num = count; I think it might be even nicer to get rid of "num" entirely and convert the cleanup path to for_each_sgtable_sg() for completeness - AFAICS it should only need an extra "if (sg_page(sg))..." check in that loop. Then "count" could possibly be squashed into its one remaining use as well, but maybe it's worth keeping for readability. Robin. > goto release; > } > } else if (dobj->page) { > @@ -418,7 +418,7 @@ armada_gem_prime_map_dma_buf(struct dma_buf_attachment *attach, > > sg_set_page(sgt->sgl, dobj->page, dobj->obj.size, 0); > > - if (dma_map_sg(attach->dev, sgt->sgl, sgt->nents, dir) == 0) > + if (dma_map_sgtable(attach->dev, sgt, dir, 0)) > goto free_table; > } else if (dobj->linear) { > /* Single contiguous physical region - no struct page */ > @@ -449,11 +449,11 @@ static void armada_gem_prime_unmap_dma_buf(struct dma_buf_attachment *attach, > int i; > > if (!dobj->linear) > - dma_unmap_sg(attach->dev, sgt->sgl, sgt->nents, dir); > + dma_unmap_sgtable(attach->dev, sgt, dir, 0); > > if (dobj->obj.filp) { > struct scatterlist *sg; > - for_each_sg(sgt->sgl, sg, sgt->nents, i) > + for_each_sgtable_sg(sgt, sg, i) > put_page(sg_page(sg)); > } > >
diff --git a/drivers/gpu/drm/armada/armada_gem.c b/drivers/gpu/drm/armada/armada_gem.c index 8005614d2e6b..bedd8937d8a1 100644 --- a/drivers/gpu/drm/armada/armada_gem.c +++ b/drivers/gpu/drm/armada/armada_gem.c @@ -395,7 +395,7 @@ armada_gem_prime_map_dma_buf(struct dma_buf_attachment *attach, mapping = dobj->obj.filp->f_mapping; - for_each_sg(sgt->sgl, sg, count, i) { + for_each_sgtable_sg(sgt, sg, i) { struct page *page; page = shmem_read_mapping_page(mapping, i); @@ -407,8 +407,8 @@ armada_gem_prime_map_dma_buf(struct dma_buf_attachment *attach, sg_set_page(sg, page, PAGE_SIZE, 0); } - if (dma_map_sg(attach->dev, sgt->sgl, sgt->nents, dir) == 0) { - num = sgt->nents; + if (dma_map_sgtable(attach->dev, sgt, dir, 0)) { + num = count; goto release; } } else if (dobj->page) { @@ -418,7 +418,7 @@ armada_gem_prime_map_dma_buf(struct dma_buf_attachment *attach, sg_set_page(sgt->sgl, dobj->page, dobj->obj.size, 0); - if (dma_map_sg(attach->dev, sgt->sgl, sgt->nents, dir) == 0) + if (dma_map_sgtable(attach->dev, sgt, dir, 0)) goto free_table; } else if (dobj->linear) { /* Single contiguous physical region - no struct page */ @@ -449,11 +449,11 @@ static void armada_gem_prime_unmap_dma_buf(struct dma_buf_attachment *attach, int i; if (!dobj->linear) - dma_unmap_sg(attach->dev, sgt->sgl, sgt->nents, dir); + dma_unmap_sgtable(attach->dev, sgt, dir, 0); if (dobj->obj.filp) { struct scatterlist *sg; - for_each_sg(sgt->sgl, sg, sgt->nents, i) + for_each_sgtable_sg(sgt, sg, i) put_page(sg_page(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. Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com> --- drivers/gpu/drm/armada/armada_gem.c | 12 ++++++------ 1 file changed, 6 insertions(+), 6 deletions(-)