Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
From:   Marek Szyprowski <m.szyprowski@samsung.com>
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>,
        "Michael J . Ruhl" <michael.j.ruhl@intel.com>
Subject: [PATCH v2] drm/prime: fix extracting of the DMA addresses from a
 scatterlist
Date:   Fri, 27 Mar 2020 17:21:26 +0100
Message-Id: <20200327162126.29705-1-m.szyprowski@samsung.com>
Content-Type: text/plain; charset="utf-8"
CMS-TYPE: 201P
References: <CGME20200327162330eucas1p1b0413e0e9887aa76d3048f86d2166dcd@eucas1p1.samsung.com>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

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