linux-kernel - [PATCH v2 2/3] drm/sun4i: dsi: fix the overhead of the horizontal front porch

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Message-Id: <20191006160303.24413-3-icenowy@aosc.io>
Date:   Mon,  7 Oct 2019 00:03:01 +0800
From:   Icenowy Zheng <icenowy@...c.io>
To:     Maxime Ripard <mripard@...nel.org>, Chen-Yu Tsai <wens@...e.org>,
        Jagan Teki <jagan@...rulasolutions.com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>
Cc:     dri-devel@...ts.freedesktop.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-sunxi@...glegroups.com, Icenowy Zheng <icenowy@...c.io>
Subject: [PATCH v2 2/3] drm/sun4i: dsi: fix the overhead of the horizontal front porch

The formula in the BSP kernel indicates that a 16-byte overhead is used
when sending the HFP. However, this value is currently set to 6 in the
sun6i_mipi_dsi driver, which makes some panels flashing.

Fix this overhead value.

Signed-off-by: Icenowy Zheng <icenowy@...c.io>
---
 drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c b/drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c
index b8a0d0501ca7..8fe8051c34e6 100644
--- a/drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c
+++ b/drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c
@@ -569,11 +569,12 @@ static void sun6i_dsi_setup_timings(struct sun6i_dsi *dsi,
 			  (mode->htotal - mode->hsync_end) * Bpp - HBP_PACKET_OVERHEAD);
 
 		/*
-		 * The frontporch is set using a blanking packet (4
-		 * bytes + payload + 2 bytes). Its minimal size is
-		 * therefore 6 bytes
+		 * The frontporch is set using a sync event (4 bytes)
+		 * and two blanking packets (each one is 4 bytes +
+		 * payload + 2 bytes). Its minimal size is therefore
+		 * 16 bytes
 		 */
-#define HFP_PACKET_OVERHEAD	6
+#define HFP_PACKET_OVERHEAD	16
 		hfp = max((unsigned int)HFP_PACKET_OVERHEAD,
 			  (mode->hsync_start - mode->hdisplay) * Bpp - HFP_PACKET_OVERHEAD);
 
-- 
2.21.0