Re: [PATCH v2] drm/prime: fix extracting of the DMA addresses from a scatterlist

On Fri, Mar 27, 2020 at 12:23 PM Marek Szyprowski m.szyprowski@samsung.com wrote:

Scatterlist elements contains both pages and DMA addresses, but one should not assume 1:1 relation between them. The sg->length is the size of the physical memory chunk described by the sg->page, while sg_dma_len(sg) is the size of the DMA (IO virtual) chunk described by the sg_dma_address(sg).

The proper way of extracting both: pages and DMA addresses of the whole buffer described by a scatterlist it to iterate independently over the sg->pages/sg->length and sg_dma_address(sg)/sg_dma_len(sg) entries.

Fixes: 42e67b479eab ("drm/prime: use dma length macro when mapping sg") Signed-off-by: Marek Szyprowski m.szyprowski@samsung.com Reviewed-by: Alex Deucher alexander.deucher@amd.com

Applied. Thanks and sorry for the breakage.

Alex

---

drivers/gpu/drm/drm_prime.c | 37 +++++++++++++++++++++++++------------ 1 file changed, 25 insertions(+), 12 deletions(-)

diff --git a/drivers/gpu/drm/drm_prime.c b/drivers/gpu/drm/drm_prime.c index 1de2cde2277c..282774e469ac 100644 --- a/drivers/gpu/drm/drm_prime.c +++ b/drivers/gpu/drm/drm_prime.c @@ -962,27 +962,40 @@ int drm_prime_sg_to_page_addr_arrays(struct sg_table *sgt, struct page **pages, unsigned count; struct scatterlist *sg; struct page *page;

•   u32 len, index;
  

•   u32 page_len, page_index;
    dma_addr_t addr;
  

•   u32 dma_len, dma_index;
  
  

•   index = 0;
  

•   /*
  

•    * Scatterlist elements contains both pages and DMA addresses, but
  

•    * one shoud not assume 1:1 relation between them. The sg->length is
  

•    * the size of the physical memory chunk described by the sg->page,
  

•    * while sg_dma_len(sg) is the size of the DMA (IO virtual) chunk
  

•    * described by the sg_dma_address(sg).
  

•    */
  

•   page_index = 0;
  

•   dma_index = 0;
    for_each_sg(sgt->sgl, sg, sgt->nents, count) {
  

•           len = sg_dma_len(sg);
  

•           page_len = sg->length;
            page = sg_page(sg);
  

•           dma_len = sg_dma_len(sg);
            addr = sg_dma_address(sg);
  
  

•           while (len > 0) {
  

•                   if (WARN_ON(index >= max_entries))
  

•           while (pages && page_len > 0) {
  

•                   if (WARN_ON(page_index >= max_entries))
                            return -1;
  

•                   if (pages)
  

•                           pages[index] = page;
  

•                   if (addrs)
  

•                           addrs[index] = addr;
  

•                   pages[page_index] = page;
                    page++;
  

•                   page_len -= PAGE_SIZE;
  

•                   page_index++;
  

•           }
  

•           while (addrs && dma_len > 0) {
  

•                   if (WARN_ON(dma_index >= max_entries))
  

•                           return -1;
  

•                   addrs[dma_index] = addr;
                    addr += PAGE_SIZE;
  

•                   len -= PAGE_SIZE;
  

•                   index++;
  

•                   dma_len -= PAGE_SIZE;
  

•                   dma_index++;
            }
    }
    return 0;
  

-- 2.17.1

---

dri-devel mailing list dri-devel@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/dri-devel