Re: [PATCH v3 01/22] drm: Include ddc adapter pointer in struct drm_connector

[Thomas Zimmermann <tzimmermann-l3A5Bk7waGM@public.gmane.org>]

Hi

I like the idea, but would prefer a more structured approach.

Setting connector->ddc before calling drm_sysfs_connector_add() seems
error prone. The dependency is not really clear from the code or interfaces.

The other thing is that drivers I mostly work on, ast and mgag200, have
code like this:

  struct ast_i2c_chan {
	struct i2c_adapter adapter;
	struct drm_device *dev;
	struct i2c_algo_bit_data bit;
  };

  struct ast_connector {
	struct drm_connector base;
	struct ast_i2c_chan *i2c;
  };

It already encodes the connection between connector and ddc adapter.

I suggest to introduce struct drm_i2c_adapter

  struct drm_i2c_adapter {
	struct i2c_adapter base;
	struct drm_connector *connector;
  };

and convert drivers over to it. Ast would look like this:

  struct ast_i2c_chan {
	struct drm_i2c_adapter adapter;
	struct i2c_algo_bit_data bit;
  };

Two new sysfs functions would set up and remove the file.

  int drm_sysfs_i2c_adapter_add(struct drm_i2c_adapter *i2c);
  void drm_sysfs_i2c_adapter_remove(struct drm_i2c_adapter *i2c);

The i2c adapter, connector->ddc pointer and sysfs entry would be
initialized by

  drm_i2c_adapter_init(struct drm_i2c_adapter *i2c, struct connector
	*connector, void *algo_data);

and cleaned up by

  drm_i2c_adapter_remove(struct drm_i2c_adapter *i2c);


Thoughts?

Best regards
Thomas

Am 28.06.19 um 18:01 schrieb Andrzej Pietrasiewicz:
> 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>
> ---
>  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
> 

-- 
Thomas Zimmermann
Graphics Driver Developer
SUSE Linux GmbH, Maxfeldstrasse 5, 90409 Nuernberg, Germany
GF: Felix Imendörffer, Mary Higgins, Sri Rasiah
HRB 21284 (AG Nürnberg)
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