linux-kernel - [PATCH v1 4/9] drm/bridge: tc358768: fix TCLK

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Date:   Thu, 27 Apr 2023 16:29:29 +0200
From:   Francesco Dolcini <francesco@...cini.it>
To:     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>,
        tomi.valkeinen@...asonboard.com, dri-devel@...ts.freedesktop.org
Cc:     Francesco Dolcini <francesco.dolcini@...adex.com>,
        David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>, linux-kernel@...r.kernel.org
Subject: [PATCH v1 4/9] drm/bridge: tc358768: fix TCLK_ZEROCNT computation

From: Francesco Dolcini <francesco.dolcini@...adex.com>

Correct computation of TCLK_ZEROCNT register.

This register must be set to a value that ensure that
(TCLK-PREPARECNT + TCLK-ZERO) > 300ns

with the actual value of (TCLK-PREPARECNT + TCLK-ZERO) being

(1 to 2) + (TCLK_ZEROCNT + 1)) x HSByteClkCycle + (PHY output delay)

with PHY output delay being about

(2 to 3) x MIPIBitClk cycle in the BitClk conversion.

Fixes: ff1ca6397b1d ("drm/bridge: Add tc358768 driver")
Signed-off-by: Francesco Dolcini <francesco.dolcini@...adex.com>
---
 drivers/gpu/drm/bridge/tc358768.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/bridge/tc358768.c b/drivers/gpu/drm/bridge/tc358768.c
index dba1bf3912f1..aff400c36066 100644
--- a/drivers/gpu/drm/bridge/tc358768.c
+++ b/drivers/gpu/drm/bridge/tc358768.c
@@ -742,10 +742,10 @@ static void tc358768_bridge_pre_enable(struct drm_bridge *bridge)
 
 	/* 38ns < TCLK_PREPARE < 95ns */
 	val = tc358768_ns_to_cnt(65, dsibclk_nsk) - 1;
-	/* TCLK_PREPARE > 300ns */
-	val2 = tc358768_ns_to_cnt(300 + tc358768_to_ns(3 * ui_nsk),
-				  dsibclk_nsk);
-	val |= (val2 - tc358768_to_ns(phy_delay_nsk - dsibclk_nsk)) << 8;
+	/* TCLK_PREPARE + TCLK_ZERO > 300ns */
+	val2 = tc358768_ns_to_cnt(300 - tc358768_to_ns(2 * ui_nsk),
+				  dsibclk_nsk) - 2;
+	val |= val2 << 8;
 	dev_dbg(priv->dev, "TCLK_HEADERCNT: 0x%x\n", val);
 	tc358768_write(priv, TC358768_TCLK_HEADERCNT, val);
 
-- 
2.25.1