drm: lima: fix common struct sg_table related issues (c3d9c17f) · Commits · 戴 / test

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> Reviewed-by:

Qiang Yu <yuq825@gmail.com>

drivers/gpu/drm/lima/lima_gem.c

+8 −3

Original line number	Diff line number	Diff line
		@@ -69,8 +69,7 @@ int lima_heap_alloc(struct lima_bo bo, struct lima_vm vm)
		return ret;

		if (bo->base.sgt) {
		dma_unmap_sg(dev, bo->base.sgt->sgl,
		bo->base.sgt->nents, DMA_BIDIRECTIONAL);
		dma_unmap_sgtable(dev, bo->base.sgt, DMA_BIDIRECTIONAL, 0);
		sg_free_table(bo->base.sgt);
		} else {
		bo->base.sgt = kmalloc(sizeof(*bo->base.sgt), GFP_KERNEL);
		@@ -80,7 +79,13 @@ int lima_heap_alloc(struct lima_bo bo, struct lima_vm vm)
		}
		}

		dma_map_sg(dev, sgt.sgl, sgt.nents, DMA_BIDIRECTIONAL);
		ret = dma_map_sgtable(dev, &sgt, DMA_BIDIRECTIONAL, 0);
		if (ret) {
		sg_free_table(&sgt);
		kfree(bo->base.sgt);
		bo->base.sgt = NULL;
		return ret;
		}

		*bo->base.sgt = sgt;

drivers/gpu/drm/lima/lima_vm.c

+2 −3

Original line number	Diff line number	Diff line
		@@ -124,7 +124,7 @@ int lima_vm_bo_add(struct lima_vm vm, struct lima_bo bo, bool create)
		if (err)
		goto err_out1;

		for_each_sg_dma_page(bo->base.sgt->sgl, &sg_iter, bo->base.sgt->nents, 0) {
		for_each_sgtable_dma_page(bo->base.sgt, &sg_iter, 0) {
		err = lima_vm_map_page(vm, sg_page_iter_dma_address(&sg_iter),
		bo_va->node.start + offset);
		if (err)
		@@ -298,8 +298,7 @@ int lima_vm_map_bo(struct lima_vm vm, struct lima_bo bo, int pageoff)
		mutex_lock(&vm->lock);

		base = bo_va->node.start + (pageoff << PAGE_SHIFT);
		for_each_sg_dma_page(bo->base.sgt->sgl, &sg_iter,
		bo->base.sgt->nents, pageoff) {
		for_each_sgtable_dma_page(bo->base.sgt, &sg_iter, pageoff) {
		err = lima_vm_map_page(vm, sg_page_iter_dma_address(&sg_iter),
		base + offset);
		if (err)

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