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Subject: Re: [PATCH v2 26/26] drm/bridge: establish a link between the
 bridge supplier and consumer
To:     Peter Rosin <peda@axentia.se>, linux-kernel@vger.kernel.org
Cc:     Archit Taneja <architt@codeaurora.org>,
        Laurent Pinchart <Laurent.pinchart@ideasonboard.com>,
        David Airlie <airlied@linux.ie>,
        Peter Senna Tschudin <peter.senna@collabora.com>,
        Martin Donnelly <martin.donnelly@ge.com>,
        Martyn Welch <martyn.welch@collabora.co.uk>,
        Gustavo Padovan <gustavo@padovan.org>,
        Maarten Lankhorst <maarten.lankhorst@linux.intel.com>,
        Sean Paul <seanpaul@chromium.org>,
        Inki Dae <inki.dae@samsung.com>,
        Joonyoung Shim <jy0922.shim@samsung.com>,
        Seung-Woo Kim <sw0312.kim@samsung.com>,
        Kyungmin Park <kyungmin.park@samsung.com>,
        Kukjin Kim <kgene@kernel.org>,
        Krzysztof Kozlowski <krzk@kernel.org>,
        CK Hu <ck.hu@mediatek.com>,
        Philipp Zabel <p.zabel@pengutronix.de>,
        Matthias Brugger <matthias.bgg@gmail.com>,
        Rob Clark <robdclark@gmail.com>,
        Sandy Huang <hjc@rock-chips.com>,
        =?UTF-8?Q?Heiko_St=c3=bcbner?= <heiko@sntech.de>,
        Benjamin Gaignard <benjamin.gaignard@linaro.org>,
        Vincent Abriou <vincent.abriou@st.com>,
        dri-devel@lists.freedesktop.org,
        linux-arm-kernel@lists.infradead.org,
        linux-samsung-soc@vger.kernel.org,
        linux-mediatek@lists.infradead.org, linux-arm-msm@vger.kernel.org,
        freedreno@lists.freedesktop.org, linux-renesas-soc@vger.kernel.org,
        linux-rockchip@lists.infradead.org, Jyri Sarha <jsarha@ti.com>,
        Daniel Vetter <daniel@ffwll.ch>
From:   Andrzej Hajda <a.hajda@samsung.com>
Message-ID: <a723ad4a-8caa-4ff5-d39d-52db98a56d7b@samsung.com>
Date:   Thu, 10 May 2018 10:10:27 +0200
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On 04.05.2018 15:52, Peter Rosin wrote:
> If the bridge supplier is unbound, this will bring the bridge consumer
> down along with the bridge. Thus, there will no longer linger any
> dangling pointers from the bridge consumer (the drm_device) to some
> non-existent bridge supplier.
>
> Signed-off-by: Peter Rosin <peda@axentia.se>
> ---
>  drivers/gpu/drm/drm_bridge.c | 18 ++++++++++++++++++
>  include/drm/drm_bridge.h     |  2 ++
>  2 files changed, 20 insertions(+)
>
> diff --git a/drivers/gpu/drm/drm_bridge.c b/drivers/gpu/drm/drm_bridge.c
> index 78d186b6831b..0259f0a3ff27 100644
> --- a/drivers/gpu/drm/drm_bridge.c
> +++ b/drivers/gpu/drm/drm_bridge.c
> @@ -26,6 +26,7 @@
>  #include <linux/mutex.h>
>  
>  #include <drm/drm_bridge.h>
> +#include <drm/drm_device.h>
>  #include <drm/drm_encoder.h>
>  
>  #include "drm_crtc_internal.h"
> @@ -127,12 +128,25 @@ int drm_bridge_attach(struct drm_encoder *encoder, struct drm_bridge *bridge,
>  	if (bridge->dev)
>  		return -EBUSY;
>  
> +	if (encoder->dev->dev != bridge->odev) {

I wonder why device_link_add does not handle this case (self dependency)
silently as noop, as it seems to be a correct behavior.

> +		bridge->link = device_link_add(encoder->dev->dev,
> +					       bridge->odev, 0);
> +		if (!bridge->link) {
> +			dev_err(bridge->odev, "failed to link bridge to %s\n",
> +				dev_name(encoder->dev->dev));
> +			return -EINVAL;
> +		}
> +	}
> +
>  	bridge->dev = encoder->dev;
>  	bridge->encoder = encoder;
>  
>  	if (bridge->funcs->attach) {
>  		ret = bridge->funcs->attach(bridge);
>  		if (ret < 0) {
> +			if (bridge->link)
> +				device_link_del(bridge->link);
> +			bridge->link = NULL;
>  			bridge->dev = NULL;
>  			bridge->encoder = NULL;
>  			return ret;
> @@ -159,6 +173,10 @@ void drm_bridge_detach(struct drm_bridge *bridge)
>  	if (bridge->funcs->detach)
>  		bridge->funcs->detach(bridge);
>  
> +	if (bridge->link)
> +		device_link_del(bridge->link);
> +	bridge->link = NULL;
> +
>  	bridge->dev = NULL;
>  }
>  
> diff --git a/include/drm/drm_bridge.h b/include/drm/drm_bridge.h
> index b656e505d11e..804189c63a4c 100644
> --- a/include/drm/drm_bridge.h
> +++ b/include/drm/drm_bridge.h
> @@ -261,6 +261,7 @@ struct drm_bridge_timings {
>   * @list: to keep track of all added bridges
>   * @timings: the timing specification for the bridge, if any (may
>   * be NULL)
> + * @link: drm consumer <-> bridge supplier

Nitpick: "<->" suggests symmetry, maybe "device link from drm consumer
to the bridge" would be better.

Anyway:
Reviewed-by: Andrzej Hajda <a.hajda@samsung.com>

 --
Regards
Andrzej

>   * @funcs: control functions
>   * @driver_private: pointer to the bridge driver's internal context
>   */
> @@ -271,6 +272,7 @@ struct drm_bridge {
>  	struct drm_bridge *next;
>  	struct list_head list;
>  	const struct drm_bridge_timings *timings;
> +	struct device_link *link;
>  
>  	const struct drm_bridge_funcs *funcs;
>  	void *driver_private;