linux-kernel - [PATCH v6 01/10] drm/vc4: hdmi: Remove the DDC probing for status detection

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Date:   Wed,  7 Jul 2021 10:47:36 +0200
From:   Maxime Ripard <maxime@...no.tech>
To:     dri-devel@...ts.freedesktop.org,
        Daniel Vetter <daniel.vetter@...el.com>,
        David Airlie <airlied@...ux.ie>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        Maxime Ripard <maxime@...no.tech>
Cc:     linux-rpi-kernel@...ts.infradead.org,
        Maxime Ripard <mripard@...nel.org>,
        Nicolas Saenz Julienne <nsaenz@...nel.org>,
        Dave Stevenson <dave.stevenson@...pberrypi.com>,
        Phil Elwell <phil@...pberrypi.com>,
        Tim Gover <tim.gover@...pberrypi.com>,
        Dom Cobley <dom@...pberrypi.com>,
        Emma Anholt <emma@...olt.net>,
        bcm-kernel-feedback-list@...adcom.com, linux-kernel@...r.kernel.org
Subject: [PATCH v6 01/10] drm/vc4: hdmi: Remove the DDC probing for status detection

Commit 9d44abbbb8d5 ("drm/vc4: Fall back to using an EDID probe in the
absence of a GPIO.") added some code to read the EDID through DDC in the
HDMI driver detect hook since the Pi3 had no HPD GPIO back then.
However, commit b1b8f45b3130 ("ARM: dts: bcm2837: Add missing GPIOs of
Expander") changed that a couple of years later.

This causes an issue though since some TV (like the LG 55C8) when it
comes out of standy will deassert the HPD line, but the EDID will
remain readable.

It causes an issues nn platforms without an HPD GPIO, like the Pi4,
where the DDC probing will be our primary mean to detect a display, and
thus we will never detect the HPD pulse. This was fine before since the
pulse was small enough that we would never detect it, and we also didn't
have anything (like the scrambler) that needed to be set up in the
display.

However, now that we have both, the display during the HPD pulse will
clear its scrambler status, and since we won't detect the
disconnect/reconnect cycle we will never enable the scrambler back.

As our main reason for that DDC probing is gone, let's just remove it.

Signed-off-by: Maxime Ripard <maxime@...no.tech>
---
 drivers/gpu/drm/vc4/vc4_hdmi.c | 2 --
 1 file changed, 2 deletions(-)

diff --git a/drivers/gpu/drm/vc4/vc4_hdmi.c b/drivers/gpu/drm/vc4/vc4_hdmi.c
index 3c4cc133e3df..8779cef13f52 100644
--- a/drivers/gpu/drm/vc4/vc4_hdmi.c
+++ b/drivers/gpu/drm/vc4/vc4_hdmi.c
@@ -169,8 +169,6 @@ vc4_hdmi_connector_detect(struct drm_connector *connector, bool force)
 	if (vc4_hdmi->hpd_gpio &&
 	    gpiod_get_value_cansleep(vc4_hdmi->hpd_gpio)) {
 		connected = true;
-	} else if (drm_probe_ddc(vc4_hdmi->ddc)) {
-		connected = true;
 	} else if (HDMI_READ(HDMI_HOTPLUG) & VC4_HDMI_HOTPLUG_CONNECTED) {
 		connected = true;
 	}
-- 
2.31.1