linux-kernel - [PATCH v2 1/2] drm/bridge: samsung-dsim: enable MFLUSH

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Message-Id: <20260208-exynos-dsim-fixes-v2-1-a857e8130a2a@disroot.org>
Date: Sun, 08 Feb 2026 00:43:58 +0530
From: Kaustabh Chakraborty <kauschluss@...root.org>
To: Inki Dae <inki.dae@...sung.com>, 
 Jagan Teki <jagan@...rulasolutions.com>, 
 Marek Szyprowski <m.szyprowski@...sung.com>, 
 Andrzej Hajda <andrzej.hajda@...el.com>, 
 Neil Armstrong <neil.armstrong@...aro.org>, Robert Foss <rfoss@...nel.org>, 
 Laurent Pinchart <Laurent.pinchart@...asonboard.com>, 
 Jonas Karlman <jonas@...boo.se>, Jernej Skrabec <jernej.skrabec@...il.com>, 
 Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>, 
 Maxime Ripard <mripard@...nel.org>, Thomas Zimmermann <tzimmermann@...e.de>, 
 David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>
Cc: dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org, 
 Kaustabh Chakraborty <kauschluss@...root.org>, stable@...r.kernel.org
Subject: [PATCH v2 1/2] drm/bridge: samsung-dsim: enable MFLUSH_VS for
 Exynos 7870 DSIM

Commit a36c533ad3e1 ("drm/bridge: samsung-dsim: Always flush display
FIFO on vsync pulse") intends to enable FIFO flushing at v-sync pulse by
not setting the active-low MFLUSH_VS bit.

However, in Exynos 7870 DSIM, the MFLUSH_VS bit is active-high. There is
no publicly available documentation to the best of my knowledge, but
downstream kernel code [1] supports this claim. Enable the bit for
Exynos 7870.

Cc: stable@...r.kernel.org # v6.17 and later
Link: https://github.com/samsungexynos7870/android_kernel_samsung_exynos7870/blob/a3762bb1761ae/drivers/video/fbdev/exynos/decon_7870/dsim_reg_7870.c#L699 [1]
Tested-by: Marek Szyprowski <m.szyprowski@...sung.com>
Signed-off-by: Kaustabh Chakraborty <kauschluss@...root.org>
---
 drivers/gpu/drm/bridge/samsung-dsim.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/drivers/gpu/drm/bridge/samsung-dsim.c b/drivers/gpu/drm/bridge/samsung-dsim.c
index 1d85e706c74b9..70f8946ad3b24 100644
--- a/drivers/gpu/drm/bridge/samsung-dsim.c
+++ b/drivers/gpu/drm/bridge/samsung-dsim.c
@@ -1089,6 +1089,13 @@ static int samsung_dsim_init_link(struct samsung_dsim *dsi)
 			reg |= DSIM_HBP_DISABLE_MODE;
 		if (dsi->mode_flags & MIPI_DSI_MODE_VIDEO_NO_HSA)
 			reg |= DSIM_HSA_DISABLE_MODE;
+
+		/*
+		 * For some hardware types, DSIM_MFLUSH_VS bit needs to be
+		 * enabled explicitly.
+		 */
+		if (dsi->plat_data->hw_type == DSIM_TYPE_EXYNOS7870)
+			reg |= DSIM_MFLUSH_VS;
 	}
 
 	if (dsi->mode_flags & MIPI_DSI_MODE_NO_EOT_PACKET)

-- 
2.52.0