linux-kernel - [PATCH 2/2] drm/bridge/tc358775: Fix DSI clock division for vsync delay calculation

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Date:   Thu, 16 Jun 2022 00:22:21 +0200
From:   Jiri Vanek <jirivanek1@...il.com>
To:     Andrzej Hajda <a.hajda@...sung.com>,
        Neil Armstrong <narmstrong@...libre.com>,
        Robert Foss <robert.foss@...aro.org>
Cc:     Vinay Simha B N <simhavcs@...il.com>,
        Laurent Pinchart <Laurent.pinchart@...asonboard.com>,
        Jonas Karlman <jonas@...boo.se>,
        Jernej Skrabec <jernej.skrabec@...il.com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        Jiri Vanek <jirivanek1@...il.com>
Subject: [PATCH 2/2] drm/bridge/tc358775: Fix DSI clock division for vsync delay calculation

Use the same PCLK divide option (divide DSI clock to generate pixel clock)
which is set to LVDS Configuration Register (LVCFG) also for a VSync delay
calculation. Without this change an auxiliary variable could underflow
during the calculation for some dual-link LVDS panels and then calculated
VSync delay is wrong. This leads to a shifted picture on a panel.

Tested-by: Jiri Vanek <jirivanek1@...il.com>
Signed-off-by: Jiri Vanek <jirivanek1@...il.com>
---
 drivers/gpu/drm/bridge/tc358775.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/bridge/tc358775.c b/drivers/gpu/drm/bridge/tc358775.c
index cd2721ab02a9..fecb8558b49a 100644
--- a/drivers/gpu/drm/bridge/tc358775.c
+++ b/drivers/gpu/drm/bridge/tc358775.c
@@ -430,7 +430,7 @@ static void tc_bridge_enable(struct drm_bridge *bridge)
 		val = TC358775_VPCTRL_MSF(1);
 
 	dsiclk = mode->crtc_clock * 3 * tc->bpc / tc->num_dsi_lanes / 1000;
-	clkdiv = dsiclk / DIVIDE_BY_3 * tc->lvds_link;
+	clkdiv = dsiclk / (tc->lvds_link == DUAL_LINK ? DIVIDE_BY_6 : DIVIDE_BY_3);
 	byteclk = dsiclk / 4;
 	t1 = hactive * (tc->bpc * 3 / 8) / tc->num_dsi_lanes;
 	t2 = ((100000 / clkdiv)) * (hactive + hback_porch + hsync_len + hfront_porch) / 1000;
-- 
2.30.2