openwrt/target/linux/bcm27xx/patches-5.4/950-0606-drm-vc4-Alter-the-HDMI-state-machine-clock-calc-to-a.patch

From 37b204f22778f51cad7bdf678d7574ff6d7508a6 Mon Sep 17 00:00:00 2001
From: Dave Stevenson <dave.stevenson@raspberrypi.com>
Date: Wed, 25 Mar 2020 18:22:40 +0000
Subject: [PATCH] drm/vc4: Alter the HDMI state machine clock calc to
 allow for 1920x1200

Whilst the documentation for BCM2835 states that the HDMI state machine
clock needs to be 108% of the pixel clock, other documentation says
that it only has to be greater than the pixel clock. The firmware
uses 101%, and that allows 1920x1200@60Hz to work within the
constraint of the HSM clock being < 163.68MHz.

Adopt 101%, and increase the maximum pixel clock for vc4 to 162MHz
so that it too supports 1920x1200@60.

Signed-off-by: Dave Stevenson <dave.stevenson@raspberrypi.com>
---
 drivers/gpu/drm/vc4/vc4_hdmi.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

--- a/drivers/gpu/drm/vc4/vc4_hdmi.c
+++ b/drivers/gpu/drm/vc4/vc4_hdmi.c
@@ -581,10 +581,11 @@ static void vc4_hdmi_encoder_enable(stru
 	}
 
 	/*
-	 * The HSM rate needs to be at 108% of the pixel clock, with a
-	 * minimum of 108MHz.
+	 * The HSM rate needs to be slightly greater than the pixel clock, with
+	 * a minimum of 108MHz.
+	 * Use 101% as this is what the firmware uses.
 	 */
-	hsm_rate = max_t(unsigned long, 108000000, (pixel_rate / 100) * 108);
+	hsm_rate = max_t(unsigned long, 108000000, (pixel_rate / 100) * 101);
 	ret = clk_set_rate(vc4_hdmi->hsm_clock, hsm_rate);
 	if (ret) {
 		DRM_ERROR("Failed to set HSM clock rate: %d\n", ret);
@@ -1731,7 +1732,7 @@ static int vc4_hdmi_dev_remove(struct pl
 }
 
 static const struct vc4_hdmi_variant bcm2835_variant = {
-	.max_pixel_clock	= 148500000,
+	.max_pixel_clock	= 162000000,
 	.audio_available	= true,
 	.cec_available		= true,
 	.registers		= vc4_hdmi_fields,