linux-kernel - [PATCH v4 29/78] drm/vc4: crtc: Add a delay after disabling the PixelValve output

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Message-Id: <a1f22aadc60a2f32022831a6348c8bbd6e1954c3.1594230107.git-series.maxime@cerno.tech>
Date:   Wed,  8 Jul 2020 19:41:37 +0200
From:   Maxime Ripard <maxime@...no.tech>
To:     Nicolas Saenz Julienne <nsaenzjulienne@...e.de>,
        Eric Anholt <eric@...olt.net>
Cc:     dri-devel@...ts.freedesktop.org,
        linux-rpi-kernel@...ts.infradead.org,
        bcm-kernel-feedback-list@...adcom.com,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Dave Stevenson <dave.stevenson@...pberrypi.com>,
        Tim Gover <tim.gover@...pberrypi.com>,
        Phil Elwell <phil@...pberrypi.com>,
        Maxime Ripard <maxime@...no.tech>
Subject: [PATCH v4 29/78] drm/vc4: crtc: Add a delay after disabling the PixelValve output

In order to avoid pixels getting stuck in the (unflushable) FIFO between
the HVS and the PV, we need to add some delay after disabling the PV output
and before disabling the HDMI controller. 20ms seems to be good enough so
let's use that.

Signed-off-by: Maxime Ripard <maxime@...no.tech>
---
 drivers/gpu/drm/vc4/vc4_crtc.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/gpu/drm/vc4/vc4_crtc.c b/drivers/gpu/drm/vc4/vc4_crtc.c
index d0b326e1df0a..7b178d67187f 100644
--- a/drivers/gpu/drm/vc4/vc4_crtc.c
+++ b/drivers/gpu/drm/vc4/vc4_crtc.c
@@ -403,6 +403,8 @@ static void vc4_crtc_atomic_disable(struct drm_crtc *crtc,
 	ret = wait_for(!(CRTC_READ(PV_V_CONTROL) & PV_VCONTROL_VIDEN), 1);
 	WARN_ONCE(ret, "Timeout waiting for !PV_VCONTROL_VIDEN\n");
 
+	mdelay(20);
+
 	if (vc4_encoder->post_crtc_disable)
 		vc4_encoder->post_crtc_disable(encoder);
 
-- 
git-series 0.9.1