linux-kernel - [PATCH 4/4] drm/bridge: lt8912b: clarify lvds output status

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Message-Id: <20220922124306.34729-5-dev@pschenker.ch>
Date:   Thu, 22 Sep 2022 14:43:06 +0200
From:   Philippe Schenker <dev@...henker.ch>
To:     dri-devel@...ts.freedesktop.org,
        Adrien Grassein <adrien.grassein@...il.com>
Cc:     Jernej Skrabec <jernej.skrabec@...il.com>,
        Jonas Karlman <jonas@...boo.se>,
        Robert Foss <robert.foss@...aro.org>,
        linux-kernel@...r.kernel.org, Daniel Vetter <daniel@...ll.ch>,
        Neil Armstrong <neil.armstrong@...aro.org>,
        Laurent Pinchart <Laurent.pinchart@...asonboard.com>,
        Andrzej Hajda <andrzej.hajda@...el.com>,
        David Airlie <airlied@...ux.ie>,
        Francesco Dolcini <francesco.dolcini@...adex.com>,
        Philippe Schenker <philippe.schenker@...adex.com>
Subject: [PATCH 4/4] drm/bridge: lt8912b: clarify lvds output status

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

Add comments on the lt8912_write_lvds_config() config to document the
current settings and to make it clear that this is a hardcoded
configuration not relevant for the HDMI output (could be removed without
affecting the HDMI port).

No changes on the actual register writes.

Signed-off-by: Francesco Dolcini <francesco.dolcini@...adex.com>
Signed-off-by: Philippe Schenker <philippe.schenker@...adex.com>
---

 drivers/gpu/drm/bridge/lontium-lt8912b.c | 26 ++++++++++++++++--------
 1 file changed, 17 insertions(+), 9 deletions(-)

diff --git a/drivers/gpu/drm/bridge/lontium-lt8912b.c b/drivers/gpu/drm/bridge/lontium-lt8912b.c
index 5968f4af190b..3e870d45f881 100644
--- a/drivers/gpu/drm/bridge/lontium-lt8912b.c
+++ b/drivers/gpu/drm/bridge/lontium-lt8912b.c
@@ -165,24 +165,32 @@ static int lt8912_write_rxlogicres_config(struct lt8912 *lt)
 	return ret;
 };
 
+/* enable LVDS output with some hardcoded configuration, not required for the HDMI output */
 static int lt8912_write_lvds_config(struct lt8912 *lt)
 {
 	const struct reg_sequence seq[] = {
+		// lvds power up
 		{0x44, 0x30},
 		{0x51, 0x05},
-		{0x50, 0x24},
-		{0x51, 0x2d},
-		{0x52, 0x04},
-		{0x69, 0x0e},
+
+		// core pll bypass
+		{0x50, 0x24}, // cp=50uA
+		{0x51, 0x2d}, // Pix_clk as reference, second order passive LPF PLL
+		{0x52, 0x04}, // loopdiv=0, use second-order PLL
+		{0x69, 0x0e}, // CP_PRESET_DIV_RATIO
 		{0x69, 0x8e},
 		{0x6a, 0x00},
-		{0x6c, 0xb8},
+		{0x6c, 0xb8}, // RGD_CP_SOFT_K_EN,RGD_CP_SOFT_K[13:8]
 		{0x6b, 0x51},
-		{0x04, 0xfb},
+
+		{0x04, 0xfb}, // core pll reset
 		{0x04, 0xff},
-		{0x7f, 0x00},
-		{0xa8, 0x13},
-		{0x02, 0xf7},
+
+		// scaler bypass
+		{0x7f, 0x00}, // disable scaler
+		{0xa8, 0x13}, // 0x13: JEIDA, 0x33: VESA
+
+		{0x02, 0xf7}, // lvds pll reset
 		{0x02, 0xff},
 		{0x03, 0xcf},
 		{0x03, 0xff},
-- 
2.37.3