linux-kernel - [PATCH] drm: remove drm_bridge_hpd_disable() from drm_bridge_connector

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Date:   Tue, 19 Sep 2023 10:48:12 -0700
From:   Abhinav Kumar <quic_abhinavk@...cinc.com>
To:     <dri-devel@...ts.freedesktop.org>,
        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>
CC:     Abhinav Kumar <quic_abhinavk@...cinc.com>,
        <freedreno@...ts.freedesktop.org>, <quic_jesszhan@...cinc.com>,
        <quic_parellan@...cinc.com>, <laurent.pinchart@...asonboard.com>,
        <andersson@...nel.org>, <jani.nikula@...ux.intel.com>,
        Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
        <linux-kernel@...r.kernel.org>
Subject: [PATCH] drm: remove drm_bridge_hpd_disable() from drm_bridge_connector_destroy()

drm_bridge_hpd_enable()/drm_bridge_hpd_disable() callbacks call into
the respective driver's hpd_enable()/hpd_disable() ops. These ops control
the HPD enable/disable logic which in some cases like MSM can be a
dedicate hardware block to control the HPD.

During probe_defer cases, a connector can be initialized and then later
destroyed till the probe is retried. During connector destroy in these
cases, the hpd_disable() callback gets called without a corresponding
hpd_enable() leading to an unbalanced state potentially causing even
a crash.

This can be avoided by the respective drivers maintaining their own
state logic to ensure that a hpd_disable() without a corresponding
hpd_enable() just returns without doing anything.

However, to have a generic fix it would be better to avoid the
hpd_disable() callback from the connector destroy path and let
the hpd_enable() / hpd_disable() balance be maintained by the
corresponding drm_bridge_connector_enable_hpd() /
drm_bridge_connector_disable_hpd() APIs which should get called by
drm_kms_helper_disable_hpd().

changes in v2:
	- minor change in commit text (Dmitry)

Signed-off-by: Abhinav Kumar <quic_abhinavk@...cinc.com>
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
---
 drivers/gpu/drm/drm_bridge_connector.c | 6 ------
 1 file changed, 6 deletions(-)

diff --git a/drivers/gpu/drm/drm_bridge_connector.c b/drivers/gpu/drm/drm_bridge_connector.c
index 1da93d5a1f61..c4dba39acfd8 100644
--- a/drivers/gpu/drm/drm_bridge_connector.c
+++ b/drivers/gpu/drm/drm_bridge_connector.c
@@ -187,12 +187,6 @@ static void drm_bridge_connector_destroy(struct drm_connector *connector)
 	struct drm_bridge_connector *bridge_connector =
 		to_drm_bridge_connector(connector);

-	if (bridge_connector->bridge_hpd) {
-		struct drm_bridge *hpd = bridge_connector->bridge_hpd;
-
-		drm_bridge_hpd_disable(hpd);
-	}
-
 	drm_connector_unregister(connector);
 	drm_connector_cleanup(connector);

-- 
2.40.1