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Date:   Tue, 25 Jun 2019 16:21:49 +0200
From:   Daniel Vetter <daniel@ffwll.ch>
To:     Andrzej Pietrasiewicz <andrzej.p@collabora.com>
Cc:     dri-devel@lists.freedesktop.org, kernel@collabora.com,
        m.szyprowski@samsung.com,
        Maarten Lankhorst <maarten.lankhorst@linux.intel.com>,
        Maxime Ripard <maxime.ripard@bootlin.com>,
        Sean Paul <sean@poorly.run>, David Airlie <airlied@linux.ie>,
        Daniel Vetter <daniel@ffwll.ch>,
        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>,
        linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
        linux-samsung-soc@vger.kernel.org
Subject: Re: [PATCH v2 1/2] drm: Include ddc adapter pointer in struct
 drm_connector
Message-ID: <20190625142149.GW12905@phenom.ffwll.local>
Mail-Followup-To: Andrzej Pietrasiewicz <andrzej.p@collabora.com>,
        dri-devel@lists.freedesktop.org, kernel@collabora.com,
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        Maarten Lankhorst <maarten.lankhorst@linux.intel.com>,
        Maxime Ripard <maxime.ripard@bootlin.com>,
        Sean Paul <sean@poorly.run>, David Airlie <airlied@linux.ie>,
        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>, linux-kernel@vger.kernel.org,
        linux-arm-kernel@lists.infradead.org,
        linux-samsung-soc@vger.kernel.org
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 <ef88f682401ae863a91e6c885d83a2756ae20b85.1561458051.git.andrzej.p@collabora.com>
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On Tue, Jun 25, 2019 at 12:24:40PM +0200, Andrzej Pietrasiewicz wrote:
> Add generic code which creates symbolic links in sysfs, pointing to ddc
> interface used by a particular video output. For example:
> 
> ls -l /sys/class/drm/card0-HDMI-A-1/ddc
> lrwxrwxrwx 1 root root 0 Jun 24 10:42 /sys/class/drm/card0-HDMI-A-1/ddc \
> 	-> ../../../../soc/13880000.i2c/i2c-2
> 
> This makes it easy for user to associate a display with its ddc adapter
> and use e.g. ddcutil to control the chosen monitor.
> 
> This patch adds an i2c_adapter pointer to struct drm_connector. Particular
> drivers can then use it instead of using their own private instance. If a
> connector contains a ddc, then create a symbolic link in sysfs.
> 
> Signed-off-by: Andrzej Pietrasiewicz <andrzej.p@collabora.com>

Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch>

As mentioned in the other subthread, I think the important bit to sell
this is rolling it out to as many drivers as feasible and collecting all
the acks from driver maintainers.
-Daniel
> ---
>  drivers/gpu/drm/drm_sysfs.c |  7 +++++++
>  include/drm/drm_connector.h | 11 +++++++++++
>  2 files changed, 18 insertions(+)
> 
> diff --git a/drivers/gpu/drm/drm_sysfs.c b/drivers/gpu/drm/drm_sysfs.c
> index ad10810bc972..26d359b39785 100644
> --- a/drivers/gpu/drm/drm_sysfs.c
> +++ b/drivers/gpu/drm/drm_sysfs.c
> @@ -294,6 +294,9 @@ int drm_sysfs_connector_add(struct drm_connector *connector)
>  	/* Let userspace know we have a new connector */
>  	drm_sysfs_hotplug_event(dev);
>  
> +	if (connector->ddc)
> +		return sysfs_create_link(&connector->kdev->kobj,
> +				 &connector->ddc->dev.kobj, "ddc");
>  	return 0;
>  }
>  
> @@ -301,6 +304,10 @@ void drm_sysfs_connector_remove(struct drm_connector *connector)
>  {
>  	if (!connector->kdev)
>  		return;
> +
> +	if (connector->ddc)
> +		sysfs_remove_link(&connector->kdev->kobj, "ddc");
> +
>  	DRM_DEBUG("removing \"%s\" from sysfs\n",
>  		  connector->name);
>  
> diff --git a/include/drm/drm_connector.h b/include/drm/drm_connector.h
> index ca745d9feaf5..1ad3d1d54ba7 100644
> --- a/include/drm/drm_connector.h
> +++ b/include/drm/drm_connector.h
> @@ -23,6 +23,7 @@
>  #ifndef __DRM_CONNECTOR_H__
>  #define __DRM_CONNECTOR_H__
>  
> +#include <linux/i2c.h>
>  #include <linux/list.h>
>  #include <linux/llist.h>
>  #include <linux/ctype.h>
> @@ -1308,6 +1309,16 @@ struct drm_connector {
>  	 * [0]: progressive, [1]: interlaced
>  	 */
>  	int audio_latency[2];
> +
> +	/**
> +	 * @ddc: associated ddc adapter.
> +	 * A connector usually has its associated ddc adapter. If a driver uses
> +	 * this field, then an appropriate symbolic link is created in connector
> +	 * sysfs directory to make it easy for the user to tell which i2c
> +	 * adapter is for a particular display.
> +	 */
> +	struct i2c_adapter *ddc;
> +
>  	/**
>  	 * @null_edid_counter: track sinks that give us all zeros for the EDID.
>  	 * Needed to workaround some HW bugs where we get all 0s
> -- 
> 2.17.1
> 

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch