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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,
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        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: <4cdcd215-8caf-e045-a478-f438f128c9f2@samsung.com>
Date:   Mon, 7 May 2018 14:59:45 +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.

I understand rationales behind this patch, but it is another step into
making drm_dev one big driver with subcomponents, where drm will work
only if every subcomponent is working/loaded. Do we need to go this way?
In case of many platforms such approach results in display turned on
very late on boot for example due to late initialization of some
regulator exposed by some i2c device, which is used by hdmi bridge. And
this hdmi bridge is just to provide alternative(rarely used) display
path, the main display path would work anyway.

So the main question to drm maintainers is about evolution of bridges,
if drm_bridges should become mandatory components of drm device or they
could be added/removed dynamically?

Regards
Andrzej


>
> 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) {
> +		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
>   * @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;