linux-kernel - [PATCH 1/1] drm: msm: Replace dma_map_sg with dma_sync

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Date:   Tue, 20 Nov 2018 15:24:37 +0530
From:   Vivek Gautam <vivek.gautam@...eaurora.org>
To:     robdclark@...il.com, airlied@...ux.ie
Cc:     linux-kernel@...r.kernel.org, freedreno@...ts.freedesktop.org,
        linux-arm-msm@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        tfiga@...omium.org, jcrouse@...eaurora.org,
        Vivek Gautam <vivek.gautam@...eaurora.org>
Subject: [PATCH 1/1] drm: msm: Replace dma_map_sg with dma_sync_sg*

dma_map_sg() expects a DMA domain. However, the drm devices
have been traditionally using unmanaged iommu domain which
is non-dma type. Using dma mapping APIs with that domain is bad.

Replace dma_map_sg() calls with dma_sync_sg_for_device{|cpu}()
to do the cache maintenance.

Signed-off-by: Vivek Gautam <vivek.gautam@...eaurora.org>
Suggested-by: Tomasz Figa <tfiga@...omium.org>
---

Tested on an MTP sdm845:
https://github.com/vivekgautam1/linux/tree/v4.19/sdm845-mtp-display-working

 drivers/gpu/drm/msm/msm_gem.c | 27 ++++++++++++++++++++-------
 1 file changed, 20 insertions(+), 7 deletions(-)

diff --git a/drivers/gpu/drm/msm/msm_gem.c b/drivers/gpu/drm/msm/msm_gem.c
index 00c795ced02c..d7a7af610803 100644
--- a/drivers/gpu/drm/msm/msm_gem.c
+++ b/drivers/gpu/drm/msm/msm_gem.c
@@ -81,6 +81,8 @@ static struct page **get_pages(struct drm_gem_object *obj)
 		struct drm_device *dev = obj->dev;
 		struct page **p;
 		int npages = obj->size >> PAGE_SHIFT;
+		struct scatterlist *s;
+		int i;
 
 		if (use_pages(obj))
 			p = drm_gem_get_pages(obj);
@@ -107,9 +109,19 @@ static struct page **get_pages(struct drm_gem_object *obj)
 		/* For non-cached buffers, ensure the new pages are clean
 		 * because display controller, GPU, etc. are not coherent:
 		 */
-		if (msm_obj->flags & (MSM_BO_WC|MSM_BO_UNCACHED))
-			dma_map_sg(dev->dev, msm_obj->sgt->sgl,
-					msm_obj->sgt->nents, DMA_BIDIRECTIONAL);
+		if (msm_obj->flags & (MSM_BO_WC | MSM_BO_UNCACHED)) {
+			/*
+			 * Fake up the SG table so that dma_sync_sg_*()
+			 * can be used to flush the pages associated with it.
+			 */
+			for_each_sg(msm_obj->sgt->sgl, s,
+				    msm_obj->sgt->nents, i)
+				sg_dma_address(s) = sg_phys(s);
+
+			dma_sync_sg_for_device(dev->dev, msm_obj->sgt->sgl,
+					       msm_obj->sgt->nents,
+					       DMA_TO_DEVICE);
+		}
 	}
 
 	return msm_obj->pages;
@@ -137,10 +149,11 @@ static void put_pages(struct drm_gem_object *obj)
 			 * pages are clean because display controller,
 			 * GPU, etc. are not coherent:
 			 */
-			if (msm_obj->flags & (MSM_BO_WC|MSM_BO_UNCACHED))
-				dma_unmap_sg(obj->dev->dev, msm_obj->sgt->sgl,
-					     msm_obj->sgt->nents,
-					     DMA_BIDIRECTIONAL);
+			if (msm_obj->flags & (MSM_BO_WC | MSM_BO_UNCACHED))
+				dma_sync_sg_for_cpu(obj->dev->dev,
+						    msm_obj->sgt->sgl,
+						    msm_obj->sgt->nents,
+						    DMA_FROM_DEVICE);
 
 			sg_free_table(msm_obj->sgt);
 			kfree(msm_obj->sgt);
-- 
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