openwrt/target/linux/bcm27xx/patches-5.15/950-0568-drm-vc4-Enable-gamma-block-only-when-required.patch

From 66d8a98666f29d7f8de926963bd4965aeeb89f13 Mon Sep 17 00:00:00 2001
From: Dave Stevenson <dave.stevenson@raspberrypi.com>
Date: Mon, 8 Nov 2021 17:32:45 +0000
Subject: [PATCH] drm/vc4: Enable gamma block only when required.

With HVS5 the gamma block is now only reprogrammed with
a disable/enable. Loading the table from vc4_hvs_init_channel
(called from vc4_hvs_atomic_enable) appears to be at an
invalid point in time and so isn't applied.

Switch to enabling and disabling the gamma table instead. This
isn't safe if the pipeline is running, but it isn't now.
For HVS4 it is safe to enable and disable dynamically, so
adopt that approach there too.

Signed-off-by: Dave Stevenson <dave.stevenson@raspberrypi.com>
---
 drivers/gpu/drm/vc4/vc4_hvs.c | 22 +++++++++++++++++-----
 1 file changed, 17 insertions(+), 5 deletions(-)

--- a/drivers/gpu/drm/vc4/vc4_hvs.c
+++ b/drivers/gpu/drm/vc4/vc4_hvs.c
@@ -503,8 +503,12 @@ static int vc4_hvs_init_channel(struct v
 	dispbkgndx &= ~SCALER_DISPBKGND_GAMMA;
 	dispbkgndx &= ~SCALER_DISPBKGND_INTERLACE;
 
+	if (crtc->state->gamma_lut)
+		/* Enable gamma on if required */
+		dispbkgndx |= SCALER_DISPBKGND_GAMMA;
+
 	HVS_WRITE(SCALER_DISPBKGNDX(chan), dispbkgndx |
-		  SCALER_DISPBKGND_AUTOHS | SCALER_DISPBKGND_GAMMA |
+		  SCALER_DISPBKGND_AUTOHS |
 		  (interlace ? SCALER_DISPBKGND_INTERLACE : 0));
 
 	/* Reload the LUT, since the SRAMs would have been disabled if
@@ -741,17 +745,25 @@ void vc4_hvs_atomic_flush(struct drm_crt
 		u32 dispbkgndx = HVS_READ(SCALER_DISPBKGNDX(vc4_state->assigned_channel));
 
 		if (crtc->state->gamma_lut) {
-			if (!vc4->hvs->hvs5)
+			if (!vc4->hvs->hvs5) {
 				vc4_hvs_update_gamma_lut(crtc);
-			else
+				dispbkgndx |= SCALER_DISPBKGND_GAMMA;
+			} else {
 				vc5_hvs_update_gamma_lut(crtc);
-			dispbkgndx |= SCALER_DISPBKGND_GAMMA;
+			}
 		} else {
 			/* Unsetting DISPBKGND_GAMMA skips the gamma lut step
 			 * in hardware, which is the same as a linear lut that
 			 * DRM expects us to use in absence of a user lut.
+			 *
+			 * Do NOT change state dynamically for hvs5 as it
+			 * inserts a delay in the pipeline that will cause
+			 * stalls if enabled/disabled whilst running. The other
+			 * should already be disabling/enabling the pipeline
+			 * when gamma changes.
 			 */
-			dispbkgndx &= ~SCALER_DISPBKGND_GAMMA;
+			if (!vc4->hvs->hvs5)
+				dispbkgndx &= ~SCALER_DISPBKGND_GAMMA;
 		}
 		HVS_WRITE(SCALER_DISPBKGNDX(vc4_state->assigned_channel), dispbkgndx);
 	}