Since commit 94fe479fae96 ("drm/rcar-du: dsi: Clean up handling of DRM mode 
flags")
the driver does not set TXVMVPRMSET0R_VSPOL_LOW and TXVMVPRMSET0R_HSPOL_LOW
for modes which set neither DRM_MODE_FLAG_[PN].SYNC. The previous behavior
was to assume that neither flag means DRM_MODE_FLAG_N.SYNC . Restore the
previous behavior for maximum compatibility.

The change of behavior is visible below, consider Vertical mode->flags
for simplicity sake, although the same applies to Horizontal ones:

Before 94fe479fae96 ("drm/rcar-du: dsi: Clean up handling of DRM mode flags") :

- DRM_MODE_FLAG_PVSYNC => vprmset0r |= 0
- DRM_MODE_FLAG_NVSYNC => vprmset0r |= TXVMVPRMSET0R_VSPOL_LOW
- Neither DRM_MODE_FLAG_[PN]VSYNC => vprmset0r |= TXVMVPRMSET0R_VSPOL_LOW

After 94fe479fae96 ("drm/rcar-du: dsi: Clean up handling of DRM mode flags") :

- DRM_MODE_FLAG_PVSYNC => vprmset0r |= 0
- DRM_MODE_FLAG_NVSYNC => vprmset0r |= TXVMVPRMSET0R_VSPOL_LOW
- Neither DRM_MODE_FLAG_[PN]VSYNC => vprmset0r |= 0 <---------- This broke

The "Neither" case behavior is different, because DRM_MODE_FLAG_N[HV]SYNC is
really not equivalent !DRM_MODE_FLAG_P[HV]SYNC .

Fixes: 94fe479fae96 ("drm/rcar-du: dsi: Clean up handling of DRM mode flags")
Signed-off-by: Marek Vasut <[email protected]>
---
Cc: David Airlie <[email protected]>
Cc: Geert Uytterhoeven <[email protected]>
Cc: Kieran Bingham <[email protected]>
Cc: Laurent Pinchart <[email protected]>
Cc: Maarten Lankhorst <[email protected]>
Cc: Magnus Damm <[email protected]>
Cc: Maxime Ripard <[email protected]>
Cc: Simona Vetter <[email protected]>
Cc: Thomas Zimmermann <[email protected]>
Cc: Tomi Valkeinen <[email protected]>
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
---
V2: - Update commit message
    - Use only !P[HV]SYNC
---
 drivers/gpu/drm/renesas/rcar-du/rcar_mipi_dsi.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/renesas/rcar-du/rcar_mipi_dsi.c 
b/drivers/gpu/drm/renesas/rcar-du/rcar_mipi_dsi.c
index 9413b76d0bfce..4ef2e3c129ed7 100644
--- a/drivers/gpu/drm/renesas/rcar-du/rcar_mipi_dsi.c
+++ b/drivers/gpu/drm/renesas/rcar-du/rcar_mipi_dsi.c
@@ -492,9 +492,9 @@ static void rcar_mipi_dsi_set_display_timing(struct 
rcar_mipi_dsi *dsi,
 
        /* Configuration for Video Parameters, input is always RGB888 */
        vprmset0r = TXVMVPRMSET0R_BPP_24;
-       if (mode->flags & DRM_MODE_FLAG_NVSYNC)
+       if (!(mode->flags & DRM_MODE_FLAG_PVSYNC))
                vprmset0r |= TXVMVPRMSET0R_VSPOL_LOW;
-       if (mode->flags & DRM_MODE_FLAG_NHSYNC)
+       if (!(mode->flags & DRM_MODE_FLAG_PHSYNC))
                vprmset0r |= TXVMVPRMSET0R_HSPOL_LOW;
 
        vprmset1r = TXVMVPRMSET1R_VACTIVE(mode->vdisplay)
-- 
2.51.0

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