linux-kernel - [PATCH 5/6] drm/msm/dpu: Require linear modifier for writeback framebuffers

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Message-Id: <20251017-b4-dpu-fixes-v1-5-40ce5993eeb6@gmail.com>
Date: Fri, 17 Oct 2025 19:58:39 +0000
From: Vladimir Lypak <vladimir.lypak@...il.com>
To: Rob Clark <robin.clark@....qualcomm.com>, 
 Dmitry Baryshkov <lumag@...nel.org>, 
 Abhinav Kumar <abhinav.kumar@...ux.dev>, 
 Jessica Zhang <jessica.zhang@....qualcomm.com>, Sean Paul <sean@...rly.run>, 
 Marijn Suijten <marijn.suijten@...ainline.org>, 
 David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>, 
 Konrad Dybcio <konrad.dybcio@....qualcomm.com>, 
 Kalyan Thota <quic_kalyant@...cinc.com>, 
 Vinod Polimera <quic_vpolimer@...cinc.com>, 
 Konrad Dybcio <konradybcio@...nel.org>, 
 Barnabás Czémán <barnabas.czeman@...nlining.org>
Cc: linux-arm-msm@...r.kernel.org, dri-devel@...ts.freedesktop.org, 
 freedreno@...ts.freedesktop.org, linux-kernel@...r.kernel.org, 
 Vladimir Lypak <vladimir.lypak@...il.com>
Subject: [PATCH 5/6] 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: 71174f362d67 ("drm/msm/dpu: move writeback's atomic_check to dpu_writeback.c")
Signed-off-by: Vladimir Lypak <vladimir.lypak@...il.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