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 Acked-by: Rob Clark robdclark@gmail.com
drivers/gpu/drm/msm/msm_gem.c | 13 +++++-------- drivers/gpu/drm/msm/msm_gpummu.c | 14 ++++++-------- drivers/gpu/drm/msm/msm_iommu.c | 2 +- 3 files changed, 12 insertions(+), 17 deletions(-)
diff --git a/drivers/gpu/drm/msm/msm_gem.c b/drivers/gpu/drm/msm/msm_gem.c index b2f49152b4d4..8c7ae812b813 100644 --- a/drivers/gpu/drm/msm/msm_gem.c +++ b/drivers/gpu/drm/msm/msm_gem.c @@ -53,11 +53,10 @@ static void sync_for_device(struct msm_gem_object *msm_obj) struct device *dev = msm_obj->base.dev->dev; if (get_dma_ops(dev) && IS_ENABLED(CONFIG_ARM64)) {
dma_sync_sg_for_device(dev, msm_obj->sgt->sgl,msm_obj->sgt->nents, DMA_BIDIRECTIONAL);
dma_sync_sgtable_for_device(dev, msm_obj->sgt,DMA_BIDIRECTIONAL);
dma_map_sg(dev, msm_obj->sgt->sgl,msm_obj->sgt->nents, DMA_BIDIRECTIONAL);
dma_map_sgtable(dev, msm_obj->sgt, DMA_BIDIRECTIONAL, 0);@@ -66,11 +65,9 @@ static void sync_for_cpu(struct msm_gem_object *msm_obj) struct device *dev = msm_obj->base.dev->dev; if (get_dma_ops(dev) && IS_ENABLED(CONFIG_ARM64)) {
dma_sync_sg_for_cpu(dev, msm_obj->sgt->sgl,msm_obj->sgt->nents, DMA_BIDIRECTIONAL);
dma_sync_sgtable_for_cpu(dev, msm_obj->sgt, DMA_BIDIRECTIONAL);
dma_unmap_sg(dev, msm_obj->sgt->sgl,msm_obj->sgt->nents, DMA_BIDIRECTIONAL);
dma_unmap_sgtable(dev, msm_obj->sgt, DMA_BIDIRECTIONAL, 0);diff --git a/drivers/gpu/drm/msm/msm_gpummu.c b/drivers/gpu/drm/msm/msm_gpummu.c index 310a31b05faa..319f06c28235 100644 --- a/drivers/gpu/drm/msm/msm_gpummu.c +++ b/drivers/gpu/drm/msm/msm_gpummu.c @@ -30,21 +30,19 @@ static int msm_gpummu_map(struct msm_mmu *mmu, uint64_t iova, { struct msm_gpummu *gpummu = to_msm_gpummu(mmu); unsigned idx = (iova - GPUMMU_VA_START) / GPUMMU_PAGE_SIZE;
- struct scatterlist *sg;
- struct sg_dma_page_iter dma_iter; unsigned prot_bits = 0;
- unsigned i, j;
if (prot & IOMMU_WRITE) prot_bits |= 1; if (prot & IOMMU_READ) prot_bits |= 2;
- for_each_sg(sgt->sgl, sg, sgt->nents, i) {
dma_addr_t addr = sg->dma_address;for (j = 0; j < sg->length / GPUMMU_PAGE_SIZE; j++, idx++) {gpummu->table[idx] = addr | prot_bits;addr += GPUMMU_PAGE_SIZE;}
- for_each_sgtable_dma_page(sgt, &dma_iter, 0) {
dma_addr_t addr = sg_page_iter_dma_address(&dma_iter);BUILD_BUG_ON(GPUMMU_PAGE_SIZE != PAGE_SIZE);gpummu->table[idx++] = addr | prot_bits;
Given that the BUILD_BUG_ON might prevent valid arm64 configs from building, how about a simple tweak like:
for (i = 0; i < PAGE_SIZE; i += GPUMMU_PAGE_SIZE) gpummu->table[idx++] = i + addr | prot_bits; ?
Or alternatively perhaps some more aggressive #ifdefs or makefile tweaks to prevent the GPUMMU code building for arm64 at all if it's only relevant to 32-bit platforms (which I believe might be the case).
Robin.
} /* we can improve by deferring flush for multiple map() */ diff --git a/drivers/gpu/drm/msm/msm_iommu.c b/drivers/gpu/drm/msm/msm_iommu.c index 3a381a9674c9..6c31e65834c6 100644 --- a/drivers/gpu/drm/msm/msm_iommu.c +++ b/drivers/gpu/drm/msm/msm_iommu.c @@ -36,7 +36,7 @@ static int msm_iommu_map(struct msm_mmu *mmu, uint64_t iova, struct msm_iommu *iommu = to_msm_iommu(mmu); size_t ret;
- ret = iommu_map_sg(iommu->domain, iova, sgt->sgl, sgt->nents, prot);
- ret = iommu_map_sgtable(iommu->domain, iova, sgt, prot); WARN_ON(!ret);
return (ret == len) ? 0 : -EINVAL;