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Subject[PATCH v2] drm/prime: fix extracting of the DMA addresses from a scatterlist
Date
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>
---
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
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