linux-kernel - [PATCH v2 2/2] drm/bridge: tc358767: Fix link properties discovery

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Date:   Wed, 08 Nov 2023 13:27:23 +0200
From:   Tomi Valkeinen <tomi.valkeinen@...asonboard.com>
To:     Aradhya Bhatia <a-bhatia1@...com>,
        Jan Kiszka <jan.kiszka@...mens.com>,
        Andrzej Hajda <andrzej.hajda@...el.com>,
        Neil Armstrong <neil.armstrong@...aro.org>,
        Robert Foss <rfoss@...nel.org>,
        Laurent Pinchart <Laurent.pinchart@...asonboard.com>,
        Jonas Karlman <jonas@...boo.se>,
        Jernej Skrabec <jernej.skrabec@...il.com>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <mripard@...nel.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>,
        Sam Ravnborg <sam@...nborg.org>
Cc:     dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        Tomi Valkeinen <tomi.valkeinen@...asonboard.com>
Subject: [PATCH v2 2/2] drm/bridge: tc358767: Fix link properties discovery

When a display controller driver uses DRM_BRIDGE_ATTACH_NO_CONNECTOR,
tc358767 will behave properly and skip the creation of the connector.

However, tc_get_display_props(), which is used to find out about the DP
monitor and link, is only called from two places: .atomic_enable() and
tc_connector_get_modes(). The latter is only used when tc358767 creates
its own connector, i.e. when DRM_BRIDGE_ATTACH_NO_CONNECTOR is _not_
set.

Thus, the driver never finds out the link properties before get_edid()
is called. With num_lanes of 0 and link_rate of 0 there are not many
valid modes...

Fix this by adding tc_get_display_props() call at the beginning of
get_edid(), so that we have up to date information before looking at the
modes.

Reported-by: Jan Kiszka <jan.kiszka@...mens.com>
Closes: https://lore.kernel.org/all/24282420-b4dd-45b3-bb1c-fc37fe4a8205@siemens.com/
Fixes: de5e6c027ae6 ("drm/bridge: tc358767: add drm_panel_bridge support")
Reviewed-by: Aradhya Bhatia <a-bhatia1@...com>
Tested-by: Jan Kiszka <jan.kiszka@...mens.com>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@...asonboard.com>
---
 drivers/gpu/drm/bridge/tc358767.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/drivers/gpu/drm/bridge/tc358767.c b/drivers/gpu/drm/bridge/tc358767.c
index 89a0d804270a..5aafbdf423c6 100644
--- a/drivers/gpu/drm/bridge/tc358767.c
+++ b/drivers/gpu/drm/bridge/tc358767.c
@@ -1579,6 +1579,13 @@ static struct edid *tc_get_edid(struct drm_bridge *bridge,
 				struct drm_connector *connector)
 {
 	struct tc_data *tc = bridge_to_tc(bridge);
+	int ret;
+
+	ret = tc_get_display_props(tc);
+	if (ret < 0) {
+		dev_err(tc->dev, "failed to read display props: %d\n", ret);
+		return 0;
+	}
 
 	return drm_get_edid(connector, &tc->aux.ddc);
 }

-- 
2.34.1