[PATCH] drm/msm/dpu: set preferred mode for writeback connector

[Abhinav Kumar]

After [1] was merged to IGT, we use either the first supported
mode in the list OR the preferred mode to determine the primary
plane to use for the sub-test due to the IGT API [2].

Since writeback does not set any preferred mode, this was
selecting 4k as that was the first entry in the list.

We use maxlinewidth to add the list of supported modes for
the writeback connector which is the right thing to do, however
since we do not have dual-SSPP support yet for DPU, this fails
the bandwidth check in dpu_core_perf_crtc_check().

Till we have dual-SSPP support, workaround this mismatch between
the list of supported modes and maxlinewidth limited modes by
marking 640x480 as the preferred mode for DPU writeback because
kms_writeback tests 640x480 mode only [3].

[1]: https://patchwork.freedesktop.org/patch/486441/
[2]: https://gitlab.freedesktop.org/drm/igt-gpu-tools/-/blob/master/lib/igt_kms.c#L1562
[3]: https://gitlab.freedesktop.org/drm/igt-gpu-tools/-/blob/master/tests/kms_writeback.c#L68

Signed-off-by: Abhinav Kumar <quic_abhinavk at quicinc.com>
---
 drivers/gpu/drm/msm/disp/dpu1/dpu_writeback.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/msm/disp/dpu1/dpu_writeback.c b/drivers/gpu/drm/msm/disp/dpu1/dpu_writeback.c
index 399115e4e217..104cc59d6466 100644
--- a/drivers/gpu/drm/msm/disp/dpu1/dpu_writeback.c
+++ b/drivers/gpu/drm/msm/disp/dpu1/dpu_writeback.c
@@ -10,9 +10,14 @@ static int dpu_wb_conn_get_modes(struct drm_connector *connector)
 	struct drm_device *dev = connector->dev;
 	struct msm_drm_private *priv = dev->dev_private;
 	struct dpu_kms *dpu_kms = to_dpu_kms(priv->kms);
+	int count;
 
-	return drm_add_modes_noedid(connector, dpu_kms->catalog->caps->max_linewidth,
+	count = drm_add_modes_noedid(connector, dpu_kms->catalog->caps->max_linewidth,
 			dev->mode_config.max_height);
+
+	drm_set_preferred_mode(connector, 640, 480);
+
+	return count;
 }
 
 static const struct drm_connector_funcs dpu_wb_conn_funcs = {
-- 
2.7.4