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    Subject[PATCH 5.9 103/391] drm: lima: fix common struct sg_table related issues
    Date
    From: Marek Szyprowski <m.szyprowski@samsung.com>

    [ Upstream commit c3d9c17f486d5c54940487dc31a54ebfdeeb371a ]

    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>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    drivers/gpu/drm/lima/lima_gem.c | 11 ++++++++---
    drivers/gpu/drm/lima/lima_vm.c | 5 ++---
    2 files changed, 10 insertions(+), 6 deletions(-)

    diff --git a/drivers/gpu/drm/lima/lima_gem.c b/drivers/gpu/drm/lima/lima_gem.c
    index 155f2b4b4030a..11223fe348dfe 100644
    --- a/drivers/gpu/drm/lima/lima_gem.c
    +++ b/drivers/gpu/drm/lima/lima_gem.c
    @@ -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;

    diff --git a/drivers/gpu/drm/lima/lima_vm.c b/drivers/gpu/drm/lima/lima_vm.c
    index 5b92fb82674a9..2b2739adc7f53 100644
    --- a/drivers/gpu/drm/lima/lima_vm.c
    +++ b/drivers/gpu/drm/lima/lima_vm.c
    @@ -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)
    --
    2.27.0


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