From: Matthew Auld <matthew.auld@intel.com>
Date: Thu, 28 Aug 2025 14:24:33 +0000 (+0100)
Subject: drm/gpusvm: use more selective dma dir in get_pages()
X-Git-Url: https://www.infradead.org/git/?a=commitdiff_plain;h=ad70e289ed4b1f87d4f158fd1ad5a3225256929d;p=users%2Fhch%2Fmisc.git

drm/gpusvm: use more selective dma dir in get_pages()

If we are only reading the memory then from the device pov the direction
can be DMA_TO_DEVICE. This aligns with the xe-userptr code. Using the
most restrictive data direction to represent the access is normally a
good idea.

Signed-off-by: Matthew Auld <matthew.auld@intel.com>
Cc: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Cc: Matthew Brost <matthew.brost@intel.com>
Reviewed-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Reviewed-by: Matthew Brost <matthew.brost@intel.com>
Link: https://lore.kernel.org/r/20250828142430.615826-12-matthew.auld@intel.com
---

diff --git a/drivers/gpu/drm/drm_gpusvm.c b/drivers/gpu/drm/drm_gpusvm.c
index 49f64d26625d..b2920b8551f5 100644
--- a/drivers/gpu/drm/drm_gpusvm.c
+++ b/drivers/gpu/drm/drm_gpusvm.c
@@ -1224,6 +1224,8 @@ int drm_gpusvm_range_get_pages(struct drm_gpusvm *gpusvm,
 	struct dev_pagemap *pagemap;
 	struct drm_pagemap *dpagemap;
 	struct drm_gpusvm_range_flags flags;
+	enum dma_data_direction dma_dir = ctx->read_only ? DMA_TO_DEVICE :
+							   DMA_BIDIRECTIONAL;
 
 retry:
 	hmm_range.notifier_seq = mmu_interval_read_begin(notifier);
@@ -1329,7 +1331,7 @@ map_pages:
 				dpagemap->ops->device_map(dpagemap,
 							  gpusvm->drm->dev,
 							  page, order,
-							  DMA_BIDIRECTIONAL);
+							  dma_dir);
 			if (dma_mapping_error(gpusvm->drm->dev,
 					      range->dma_addr[j].addr)) {
 				err = -EFAULT;
@@ -1351,7 +1353,7 @@ map_pages:
 			addr = dma_map_page(gpusvm->drm->dev,
 					    page, 0,
 					    PAGE_SIZE << order,
-					    DMA_BIDIRECTIONAL);
+					    dma_dir);
 			if (dma_mapping_error(gpusvm->drm->dev, addr)) {
 				err = -EFAULT;
 				goto err_unmap;
@@ -1359,7 +1361,7 @@ map_pages:
 
 			range->dma_addr[j] = drm_pagemap_addr_encode
 				(addr, DRM_INTERCONNECT_SYSTEM, order,
-				 DMA_BIDIRECTIONAL);
+				 dma_dir);
 		}
 		i += 1 << order;
 		num_dma_mapped = i;