linux-kernel - [PATCH V3] drm/amdgpu: limit DMA size to PAGE

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Date:   Wed, 11 Apr 2018 18:11:22 -0400
From:   Sinan Kaya <okaya@...eaurora.org>
To:     amd-gfx@...ts.freedesktop.org, sulrich@...eaurora.org,
        timur@...eaurora.org
Cc:     linux-arm-msm@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        Sinan Kaya <okaya@...eaurora.org>,
        Alex Deucher <alexander.deucher@....com>,
        Christian König <christian.koenig@....com>,
        "David (ChunMing) Zhou" <David1.Zhou@....com>,
        David Airlie <airlied@...ux.ie>, Monk Liu <Monk.Liu@....com>,
        Harry Wentland <harry.wentland@....com>,
        Pixel Ding <Pixel.Ding@....com>,
        Horace Chen <horace.chen@....com>,
        dri-devel@...ts.freedesktop.org (open list:DRM DRIVERS),
        linux-kernel@...r.kernel.org (open list)
Subject: [PATCH V3] drm/amdgpu: limit DMA size to PAGE_SIZE for scatter-gather buffers

Code is expecing to observe the same number of buffers returned from
dma_map_sg() function compared to sg_alloc_table_from_pages(). This
doesn't hold true universally especially for systems with IOMMU.

The hardware actually needs the dma_address on a page by page basis.
Joining multiple consecutive pages into one entry is just additional
overhead which we don't need.

Signed-off-by: Sinan Kaya <okaya@...eaurora.org>
---
 drivers/gpu/drm/amd/amdgpu/amdgpu_device.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_device.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_device.c
index af1b879..91abe1a 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_device.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_device.c
@@ -1948,6 +1948,9 @@ int amdgpu_device_init(struct amdgpu_device *adev,
 	/* init the mode config */
 	drm_mode_config_init(adev->ddev);
 
+	/* limit scatter-gather buffer size to PAGE_SIZE */
+	dma_set_max_seg_size(adev->dev, PAGE_SIZE);
+
 	r = amdgpu_device_ip_init(adev);
 	if (r) {
 		/* failed in exclusive mode due to timeout */
-- 
2.7.4