From a00957efee9643c3b025b9d20d6ab4fc6536eb89 Mon Sep 17 00:00:00 2001
From: Michael Forney <mforney@mforney.org>
Date: Wed, 2 Mar 2022 10:26:36 +0000
Subject: [PATCH] igfx: maintain single/double-channel LVDS mode from BIOS

---
 sys/src/cmd/aux/vga/igfx.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/sys/src/cmd/aux/vga/igfx.c b/sys/src/cmd/aux/vga/igfx.c
index 58919bea4..bacfb493c 100644
--- a/sys/src/cmd/aux/vga/igfx.c
+++ b/sys/src/cmd/aux/vga/igfx.c
@@ -850,7 +850,12 @@ initdpll(Igfx *igfx, int x, int freq, int port)
 	dpll->ctrl.v &= ~(3<<24);
 	if(port == PortLCD){
 		p2 = 14;
-		if(freq > 112*MHz){
+		/*
+		 * Use dual-channel LVDS if the display clock is
+		 * outside the range of single-channel, or it was
+		 * preconfigured by the BIOS.
+		 */
+		if(freq > 112*MHz || (igfx->lvds.v>>4 & 3) == 3){
 			p2 >>= 1;
 			dpll->ctrl.v |= (1<<24);
 		}