-----Original Message----- From: Marek Szyprowski m.szyprowski@samsung.com Sent: Friday, March 27, 2020 12:21 PM To: dri-devel@lists.freedesktop.org; linux-samsung-soc@vger.kernel.org; linux-kernel@vger.kernel.org Cc: Marek Szyprowski m.szyprowski@samsung.com; stable@vger.kernel.org; Bartlomiej Zolnierkiewicz b.zolnierkie@samsung.com; Maarten Lankhorst maarten.lankhorst@linux.intel.com; Maxime Ripard mripard@kernel.org; Thomas Zimmermann tzimmermann@suse.de; David Airlie airlied@linux.ie; Daniel Vetter daniel@ffwll.ch; Alex Deucher alexander.deucher@amd.com; Shane Francis bigbeeshane@gmail.com; Ruhl, Michael J michael.j.ruhl@intel.com Subject: [PATCH v2] drm/prime: fix extracting of the DMA addresses from a scatterlist
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->lengthis
* 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).*/
Is there an example of what the scatterlist would look like in this case?
Does each SG entry always have the page and dma info? or could you have entries that have page information only, and entries that have dma info only?
If the same entry has different size info (page_len = PAGE_SIZE, dma_len = 4 * PAGE_SIZE?), are we guaranteed that the arrays (page and addrs) have been sized correctly?
Just trying to get my head wrapped around this.
Thanks,
Mike
- page_index = 0;
- dma_index = 0; for_each_sg(sgt->sgl, sg, sgt->nents, count) {
len = sg_dma_len(sg);
page_len = sg->length;dma_len = sg_dma_len(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++;-- 2.17.1