UBWC-related register configuration for writeback is not implemented in
the driver yet but there aren't any checks for non-linear modifiers in
atomic_check. Thus when compressed framebuffer is attached to writeback
connector it will be filled with linear image data. This patch forbids
non-linear modifiers for writeback framebuffers until UBWC support for
writeback is properly implemented.

Fixes: 71174f362d67 ("drm/msm/dpu: move writeback's atomic_check to dpu_writeback.c")
Signed-off-by: Vladimir Lypak <vladimir.lypak@gmail.com>
---
 drivers/gpu/drm/msm/disp/dpu1/dpu_writeback.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/gpu/drm/msm/disp/dpu1/dpu_writeback.c b/drivers/gpu/drm/msm/disp/dpu1/dpu_writeback.c
index cd73468e369a93c50303db2a7d4499bcb17be5d1..7545c0293efbd8f7eb34a4ac56f616b7cadae1c0 100644
--- a/drivers/gpu/drm/msm/disp/dpu1/dpu_writeback.c
+++ b/drivers/gpu/drm/msm/disp/dpu1/dpu_writeback.c
@@ -72,6 +72,9 @@ static int dpu_wb_conn_atomic_check(struct drm_connector *connector,
 		DPU_ERROR("invalid fb w=%d, maxlinewidth=%u\n",
 			  fb->width, dpu_wb_conn->maxlinewidth);
 		return -EINVAL;
+	} else if (fb->modifier != DRM_FORMAT_MOD_LINEAR) {
+		DPU_ERROR("unsupported fb modifier:%#llx\n", fb->modifier);
+		return -EINVAL;
 	}
 
 	return drm_atomic_helper_check_wb_connector_state(conn_state->connector, conn_state->state);

-- 
2.51.0

On Fri, Oct 17, 2025 at 07:58:39PM +0000, Vladimir Lypak wrote:
> UBWC-related register configuration for writeback is not implemented in
> the driver yet but there aren't any checks for non-linear modifiers in
> atomic_check. Thus when compressed framebuffer is attached to writeback
> connector it will be filled with linear image data. This patch forbids
> non-linear modifiers for writeback framebuffers until UBWC support for
> writeback is properly implemented.
> 
> Fixes: 71174f362d67 ("drm/msm/dpu: move writeback's atomic_check to dpu_writeback.c")
> Signed-off-by: Vladimir Lypak <vladimir.lypak@gmail.com>
> ---
>  drivers/gpu/drm/msm/disp/dpu1/dpu_writeback.c | 3 +++
>  1 file changed, 3 insertions(+)
> 

Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com>


-- 
With best wishes
Dmitry