[PATCH] drm/xe/display: fix ttm_bo_access() usage

[Matthew Auld <matthew.auld@intel.com>]

ttm_bo_access() returns the size on success. Account for that otherwise
the caller incorrectly thinks this is an error in
intel_atomic_prepare_plane_clear_colors().

Fixes: b6308aaa24a7 ("drm/xe/display: Update intel_bo_read_from_page to use ttm_bo_access")
Link: https://gitlab.freedesktop.org/drm/xe/kernel/-/issues/3661
Signed-off-by: Matthew Auld <matthew.auld@intel.com>
Cc: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Cc: Matthew Brost <matthew.brost@intel.com>
Cc: Jani Nikula <jani.nikula@intel.com>
---
 drivers/gpu/drm/xe/display/intel_bo.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/xe/display/intel_bo.c b/drivers/gpu/drm/xe/display/intel_bo.c
index 43141964f6f2..b2a8d06cc78a 100644
--- a/drivers/gpu/drm/xe/display/intel_bo.c
+++ b/drivers/gpu/drm/xe/display/intel_bo.c
@@ -40,8 +40,13 @@ int intel_bo_fb_mmap(struct drm_gem_object *obj, struct vm_area_struct *vma)
 int intel_bo_read_from_page(struct drm_gem_object *obj, u64 offset, void *dst, int size)
 {
 	struct xe_bo *bo = gem_to_xe_bo(obj);
+	int ret;
 
-	return ttm_bo_access(&bo->ttm, offset, dst, size, 0);
+	ret = ttm_bo_access(&bo->ttm, offset, dst, size, 0);
+	if (ret == size)
+		ret = 0;
+
+	return ret;
 }
 
 struct intel_frontbuffer *intel_bo_get_frontbuffer(struct drm_gem_object *obj)
-- 
2.47.0