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

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Date:   Tue, 18 Jul 2023 08:55:30 +0300
From:   Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To:     Abhinav Kumar <quic_abhinavk@...cinc.com>,
        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:     freedreno@...ts.freedesktop.org, robdclark@...il.com,
        quic_jesszhan@...cinc.com, laurent.pinchart@...asonboard.com,
        andersson@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drm: remove drm_bridge_hpd_disable() from
 drm_bridge_connector_destroy()

On 18/07/2023 01:34, Abhinav Kumar wrote:
> 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 the drm_kms_helper_disable_hpd().

Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>

> 
> Signed-off-by: Abhinav Kumar <quic_abhinavk@...cinc.com>
> ---
>   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 19ae4a177ac3..3d4e25c2f3d7 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);
>   

-- 
With best wishes
Dmitry