linux-kernel - [PATCH AUTOSEL 5.15 30/69] drm/bridge/tc358775: Fix DSI clock division for vsync delay calculation

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Date:   Thu, 11 Aug 2022 11:55:39 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Jiri Vanek <jirivanek1@...il.com>,
        Vinay Simha BN <simhavcs@...il.com>,
        Robert Foss <robert.foss@...aro.org>,
        Sasha Levin <sashal@...nel.org>, andrzej.hajda@...el.com,
        narmstrong@...libre.com, airlied@...ux.ie, daniel@...ll.ch,
        dri-devel@...ts.freedesktop.org
Subject: [PATCH AUTOSEL 5.15 30/69] drm/bridge/tc358775: Fix DSI clock division for vsync delay calculation

From: Jiri Vanek <jirivanek1@...il.com>

[ Upstream commit 993a87917c2af59efb0ee1ce43c878ca8790ba1c ]

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>
Reviewed-by: Vinay Simha BN <simhavcs@...il.com>
Signed-off-by: Robert Foss <robert.foss@...aro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20220615222221.1501-3-jirivanek1@gmail.com
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 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 2272adcc5b4a..70b6210c9803 100644
--- a/drivers/gpu/drm/bridge/tc358775.c
+++ b/drivers/gpu/drm/bridge/tc358775.c
@@ -429,7 +429,7 @@ 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;
-- 
2.35.1