linux-kernel - Re: [PATCH 2/2] media/Documentation: Volatile writable

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Message-ID: <54E355BC.9070803@xs4all.nl>
Date:	Tue, 17 Feb 2015 15:52:44 +0100
From:	Hans Verkuil <hverkuil@...all.nl>
To:	Ricardo Ribalda Delgado <ricardo.ribalda@...il.com>,
	Hans Verkuil <hans.verkuil@...co.com>,
	Mauro Carvalho Chehab <mchehab@....samsung.com>,
	Jonathan Corbet <corbet@....net>,
	Arun Kumar K <arun.kk@...sung.com>,
	Sylwester Nawrocki <s.nawrocki@...sung.com>,
	Sakari Ailus <sakari.ailus@...ux.intel.com>,
	Antti Palosaari <crope@....fi>, linux-media@...r.kernel.org,
	linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] media/Documentation: Volatile writable

On 02/17/2015 03:41 PM, Ricardo Ribalda Delgado wrote:
> Volatile variables are also writable now. Update the documentation
> accordingly.
> 
> Signed-off-by: Ricardo Ribalda Delgado <ricardo.ribalda@...il.com>
> ---
>  Documentation/DocBook/media/v4l/vidioc-dqevent.xml   | 7 ++++---
>  Documentation/DocBook/media/v4l/vidioc-queryctrl.xml | 6 ++++--
>  Documentation/video4linux/v4l2-controls.txt          | 4 +++-
>  3 files changed, 11 insertions(+), 6 deletions(-)
> 
> diff --git a/Documentation/DocBook/media/v4l/vidioc-dqevent.xml b/Documentation/DocBook/media/v4l/vidioc-dqevent.xml
> index b036f89..38d907e 100644
> --- a/Documentation/DocBook/media/v4l/vidioc-dqevent.xml
> +++ b/Documentation/DocBook/media/v4l/vidioc-dqevent.xml
> @@ -318,9 +318,10 @@
>  	    <entry><constant>V4L2_EVENT_CTRL_CH_VALUE</constant></entry>
>  	    <entry>0x0001</entry>
>  	    <entry>This control event was triggered because the value of the control
> -		changed. Special case: if a button control is pressed, then this
> -		event is sent as well, even though there is not explicit value
> -		associated with a button control.</entry>
> +		changed. Special cases: Volatile controls do no generate this event;

Volatile -> volatile
no -> not
event; -> event.

> +		If a button control is pressed, then this event is sent as well,
> +		even though there is not explicit value associated with a button

Hmm: not -> no

:-)

> +		control.</entry>
>  	  </row>
>  	  <row>
>  	    <entry><constant>V4L2_EVENT_CTRL_CH_FLAGS</constant></entry>
> diff --git a/Documentation/DocBook/media/v4l/vidioc-queryctrl.xml b/Documentation/DocBook/media/v4l/vidioc-queryctrl.xml
> index 2bd98fd..6e1e98d 100644
> --- a/Documentation/DocBook/media/v4l/vidioc-queryctrl.xml
> +++ b/Documentation/DocBook/media/v4l/vidioc-queryctrl.xml
> @@ -599,8 +599,10 @@ writing a value will cause the device to carry out a given action
>  	    <entry>This control is volatile, which means that the value of the control
>  changes continuously. A typical example would be the current gain value if the device
>  is in auto-gain mode. In such a case the hardware calculates the gain value based on
> -the lighting conditions which can change over time. Note that setting a new value for
> -a volatile control will have no effect. The new value will just be ignored.</entry>
> +the lighting conditions which can change over time. Another example would be an error
> +flag (missed trigger, invalid voltage on the sensor). In those situations the user
> +could write to the control to acknowledge the error, but that write will never
> +generate a <constant>V4L2_EVENT_CTRL_CH_VALUE</constant> event.<entry>
>  	  </row>
>  	  <row>
>  	    <entry><constant>V4L2_CTRL_FLAG_HAS_PAYLOAD</constant></entry>
> diff --git a/Documentation/video4linux/v4l2-controls.txt b/Documentation/video4linux/v4l2-controls.txt
> index 0f84ce8..5517db6 100644
> --- a/Documentation/video4linux/v4l2-controls.txt
> +++ b/Documentation/video4linux/v4l2-controls.txt
> @@ -344,7 +344,9 @@ implement g_volatile_ctrl like this:
>  	}
>  
>  Note that you use the 'new value' union as well in g_volatile_ctrl. In general
> -controls that need to implement g_volatile_ctrl are read-only controls.
> +controls that need to implement g_volatile_ctrl are read-only controls. If they
> +are not, a V4L2_EVENT_CTRL_CH_VALUE will not be generated when the control
> +changes.
>  
>  To mark a control as volatile you have to set V4L2_CTRL_FLAG_VOLATILE:
>  
> 

With those typo fixes:

Acked-by: Hans Verkuil <hans.verkuil@...co.com>

Thanks!

	Hans
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