linux-kernel - Re: [PATCH 3/3] Revert "drm/bridge: panel: Add a device link between drm device and panel device"

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Message-ID: <6e235fe1-d2ab-4a57-9f31-f16c22de5093@linaro.org>
Date:   Tue, 28 Nov 2023 09:24:58 +0100
From:   Neil Armstrong <neil.armstrong@...aro.org>
To:     Linus Walleij <linus.walleij@...aro.org>,
        Liu Ying <victor.liu@....com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Andrzej Hajda <andrzej.hajda@...el.com>,
        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>
Cc:     linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org
Subject: Re: [PATCH 3/3] Revert "drm/bridge: panel: Add a device link between
 drm device and panel device"

On 28/11/2023 00:10, Linus Walleij wrote:
> This reverts commit 199cf07ebd2b0d41185ac79b895547d45610b681.
> 
> This patch creates bugs on devices where the DRM device is
> the ancestor of the panel devices.
> 
> Attempts to fix this have failed because it leads to using
> device core functionality which is questionable.
> 
> Reported-by: Linus Walleij <linus.walleij@...aro.org>
> Link: https://lore.kernel.org/lkml/CACRpkdaGzXD6HbiX7mVUNJAJtMEPG00Pp6+nJ1P0JrfJ-ArMvQ@mail.gmail.com/T/
> Signed-off-by: Linus Walleij <linus.walleij@...aro.org>
> ---
>   drivers/gpu/drm/bridge/panel.c | 17 -----------------
>   1 file changed, 17 deletions(-)
> 
> diff --git a/drivers/gpu/drm/bridge/panel.c b/drivers/gpu/drm/bridge/panel.c
> index e48823a4f1ed..7f41525f7a6e 100644
> --- a/drivers/gpu/drm/bridge/panel.c
> +++ b/drivers/gpu/drm/bridge/panel.c
> @@ -4,8 +4,6 @@
>    * Copyright (C) 2017 Broadcom
>    */
>   
> -#include <linux/device.h>
> -
>   #include <drm/drm_atomic_helper.h>
>   #include <drm/drm_bridge.h>
>   #include <drm/drm_connector.h>
> @@ -21,7 +19,6 @@ struct panel_bridge {
>   	struct drm_bridge bridge;
>   	struct drm_connector connector;
>   	struct drm_panel *panel;
> -	struct device_link *link;
>   	u32 connector_type;
>   };
>   
> @@ -63,24 +60,13 @@ static int panel_bridge_attach(struct drm_bridge *bridge,
>   {
>   	struct panel_bridge *panel_bridge = drm_bridge_to_panel_bridge(bridge);
>   	struct drm_connector *connector = &panel_bridge->connector;
> -	struct drm_panel *panel = panel_bridge->panel;
> -	struct drm_device *drm_dev = bridge->dev;
>   	int ret;
>   
> -	panel_bridge->link = device_link_add(drm_dev->dev, panel->dev,
> -					     DL_FLAG_STATELESS);
> -	if (!panel_bridge->link) {
> -		DRM_ERROR("Failed to add device link between %s and %s\n",
> -			  dev_name(drm_dev->dev), dev_name(panel->dev));
> -		return -EINVAL;
> -	}
> -
>   	if (flags & DRM_BRIDGE_ATTACH_NO_CONNECTOR)
>   		return 0;
>   
>   	if (!bridge->encoder) {
>   		DRM_ERROR("Missing encoder\n");
> -		device_link_del(panel_bridge->link);
>   		return -ENODEV;
>   	}
>   
> @@ -92,7 +78,6 @@ static int panel_bridge_attach(struct drm_bridge *bridge,
>   				 panel_bridge->connector_type);
>   	if (ret) {
>   		DRM_ERROR("Failed to initialize connector\n");
> -		device_link_del(panel_bridge->link);
>   		return ret;
>   	}
>   
> @@ -115,8 +100,6 @@ static void panel_bridge_detach(struct drm_bridge *bridge)
>   	struct panel_bridge *panel_bridge = drm_bridge_to_panel_bridge(bridge);
>   	struct drm_connector *connector = &panel_bridge->connector;
>   
> -	device_link_del(panel_bridge->link);
> -
>   	/*
>   	 * Cleanup the connector if we know it was initialized.
>   	 *
> 

Acked-by: Neil Armstrong <neil.armstrong@...aro.org>