950-0262-drm-vc4-Limit-fkms-to-modes-85Hz.patch

From 9f9d67a11cfd6318d2bd1321090c0950242cfa25 Mon Sep 17 00:00:00 2001
From: Dave Stevenson <dave.stevenson@raspberrypi.org>
Date: Tue, 18 Jun 2019 21:37:45 +0100
Subject: [PATCH] drm/vc4: Limit fkms to modes <= 85Hz

Selecting 1080p100 and 120 has very limited gain, but don't want
to block VGA85 and similar.

Signed-off-by: Dave Stevenson <dave.stevenson@raspberrypi.org>
---
 drivers/gpu/drm/vc4/vc4_firmware_kms.c | 4 ++++
 1 file changed, 4 insertions(+)

--- a/drivers/gpu/drm/vc4/vc4_firmware_kms.c
+++ b/drivers/gpu/drm/vc4/vc4_firmware_kms.c
@@ -823,6 +823,10 @@ vc4_crtc_mode_valid(struct drm_crtc *crt
 		return MODE_NO_DBLESCAN;
 	}
 
+	/* Disable refresh rates > 85Hz as limited gain from them */
+	if (drm_mode_vrefresh(mode) > 85)
+		return MODE_BAD_VVALUE;
+
 	/* Limit the pixel clock based on the HDMI clock limits from the
 	 * firmware
 	 */