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    SubjectRe: [Linux-graphics-maintainer] [PATCH v3 15/25] drm: vmwgfx: fix common struct sg_table related issues
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    I'm not exactly an expert on this, but looks alright to me.
    Acked-by: Roland Scheidegger <sroland@vmware.com>

    Am 05.05.20 um 10:46 schrieb Marek Szyprowski:
    > The Documentation/DMA-API-HOWTO.txt states that dma_map_sg returns the
    > numer of the created entries in the DMA address space. However the
    > subsequent calls to dma_sync_sg_for_{device,cpu} and dma_unmap_sg must be
    > called with the original number of the entries passed to dma_map_sg. The
    > sg_table->nents in turn holds the result of the dma_map_sg call as stated
    > in include/linux/scatterlist.h. A common mistake was to ignore a result
    > of the dma_map_sg function and don't use the sg_table->orig_nents at all.
    >
    > To avoid such issues, lets use common dma-mapping wrappers operating
    > directly on the struct sg_table objects and adjust references to the
    > nents and orig_nents respectively.
    >
    > Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
    > ---
    > For more information, see '[PATCH v3 00/25] DRM: fix struct sg_table nents
    > vs. orig_nents misuse' thread: https://lkml.org/lkml/2020/5/5/187
    > ---
    > drivers/gpu/drm/vmwgfx/vmwgfx_ttm_buffer.c | 17 ++++-------------
    > 1 file changed, 4 insertions(+), 13 deletions(-)
    >
    > diff --git a/drivers/gpu/drm/vmwgfx/vmwgfx_ttm_buffer.c b/drivers/gpu/drm/vmwgfx/vmwgfx_ttm_buffer.c
    > index bf0bc46..e50ae8b 100644
    > --- a/drivers/gpu/drm/vmwgfx/vmwgfx_ttm_buffer.c
    > +++ b/drivers/gpu/drm/vmwgfx/vmwgfx_ttm_buffer.c
    > @@ -362,8 +362,7 @@ static void vmw_ttm_unmap_from_dma(struct vmw_ttm_tt *vmw_tt)
    > {
    > struct device *dev = vmw_tt->dev_priv->dev->dev;
    >
    > - dma_unmap_sg(dev, vmw_tt->sgt.sgl, vmw_tt->sgt.nents,
    > - DMA_BIDIRECTIONAL);
    > + dma_unmap_sgtable(dev, vmw_tt->sgt, DMA_BIDIRECTIONAL);
    > vmw_tt->sgt.nents = vmw_tt->sgt.orig_nents;
    > }
    >
    > @@ -383,16 +382,8 @@ static void vmw_ttm_unmap_from_dma(struct vmw_ttm_tt *vmw_tt)
    > static int vmw_ttm_map_for_dma(struct vmw_ttm_tt *vmw_tt)
    > {
    > struct device *dev = vmw_tt->dev_priv->dev->dev;
    > - int ret;
    > -
    > - ret = dma_map_sg(dev, vmw_tt->sgt.sgl, vmw_tt->sgt.orig_nents,
    > - DMA_BIDIRECTIONAL);
    > - if (unlikely(ret == 0))
    > - return -ENOMEM;
    >
    > - vmw_tt->sgt.nents = ret;
    > -
    > - return 0;
    > + return dma_map_sgtable(dev, vmw_tt->sgt, DMA_BIDIRECTIONAL);
    > }
    >
    > /**
    > @@ -449,10 +440,10 @@ static int vmw_ttm_map_dma(struct vmw_ttm_tt *vmw_tt)
    > if (unlikely(ret != 0))
    > goto out_sg_alloc_fail;
    >
    > - if (vsgt->num_pages > vmw_tt->sgt.nents) {
    > + if (vsgt->num_pages > vmw_tt->sgt.orig_nents) {
    > uint64_t over_alloc =
    > sgl_size * (vsgt->num_pages -
    > - vmw_tt->sgt.nents);
    > + vmw_tt->sgt.orig_nents);
    >
    > ttm_mem_global_free(glob, over_alloc);
    > vmw_tt->sg_alloc_size -= over_alloc;
    >

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