drm/msm/dpu: Require linear modifier for writeback framebuffers

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: 71174f3 ("drm/msm/dpu: move writeback's atomic_check to dpu_writeback.c")
Signed-off-by: Vladimir Lypak <[email protected]>
Reviewed-by: Dmitry Baryshkov <[email protected]>
Patchwork: https://patchwork.freedesktop.org/patch/681922/
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Dmitry Baryshkov <[email protected]>

Author: vldly

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);