linux-kernel - Re: [PATCH v4 14/36] [media] v4l2-mc: add a function to inherit controls from a pipeline

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Date:   Thu, 2 Mar 2017 18:12:43 -0800
From:   Steve Longerbeam <slongerbeam@...il.com>
To:     Sakari Ailus <sakari.ailus@....fi>
Cc:     robh+dt@...nel.org, mark.rutland@....com, shawnguo@...nel.org,
        kernel@...gutronix.de, fabio.estevam@....com,
        linux@...linux.org.uk, mchehab@...nel.org, hverkuil@...all.nl,
        nick@...anahar.org, markus.heiser@...marIT.de,
        p.zabel@...gutronix.de, laurent.pinchart+renesas@...asonboard.com,
        bparrot@...com, geert@...ux-m68k.org, arnd@...db.de,
        sudipm.mukherjee@...il.com, minghsiu.tsai@...iatek.com,
        tiffany.lin@...iatek.com, jean-christophe.trotin@...com,
        horms+renesas@...ge.net.au, niklas.soderlund+renesas@...natech.se,
        robert.jarzmik@...e.fr, songjun.wu@...rochip.com,
        andrew-ct.chen@...iatek.com, gregkh@...uxfoundation.org,
        shuah@...nel.org, sakari.ailus@...ux.intel.com, pavel@....cz,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-media@...r.kernel.org,
        devel@...verdev.osuosl.org,
        Steve Longerbeam <steve_longerbeam@...tor.com>
Subject: Re: [PATCH v4 14/36] [media] v4l2-mc: add a function to inherit
 controls from a pipeline



On 03/02/2017 03:48 PM, Steve Longerbeam wrote:
>
>
> On 03/02/2017 08:02 AM, Sakari Ailus wrote:
>> Hi Steve,
>>
>> On Wed, Feb 15, 2017 at 06:19:16PM -0800, Steve Longerbeam wrote:
>>> v4l2_pipeline_inherit_controls() will add the v4l2 controls from
>>> all subdev entities in a pipeline to a given video device.
>>>
>>> Signed-off-by: Steve Longerbeam <steve_longerbeam@...tor.com>
>>> ---
>>>  drivers/media/v4l2-core/v4l2-mc.c | 48
>>> +++++++++++++++++++++++++++++++++++++++
>>>  include/media/v4l2-mc.h           | 25 ++++++++++++++++++++
>>>  2 files changed, 73 insertions(+)
>>>
>>> diff --git a/drivers/media/v4l2-core/v4l2-mc.c
>>> b/drivers/media/v4l2-core/v4l2-mc.c
>>> index 303980b..09d4d97 100644
>>> --- a/drivers/media/v4l2-core/v4l2-mc.c
>>> +++ b/drivers/media/v4l2-core/v4l2-mc.c
>>> @@ -22,6 +22,7 @@
>>>  #include <linux/usb.h>
>>>  #include <media/media-device.h>
>>>  #include <media/media-entity.h>
>>> +#include <media/v4l2-ctrls.h>
>>>  #include <media/v4l2-fh.h>
>>>  #include <media/v4l2-mc.h>
>>>  #include <media/v4l2-subdev.h>
>>> @@ -238,6 +239,53 @@ int v4l_vb2q_enable_media_source(struct
>>> vb2_queue *q)
>>>  }
>>>  EXPORT_SYMBOL_GPL(v4l_vb2q_enable_media_source);
>>>
>>> +int __v4l2_pipeline_inherit_controls(struct video_device *vfd,
>>> +                     struct media_entity *start_entity)
>>
>> I have a few concerns / questions:
>>
>> - What's the purpose of this patch? Why not to access the sub-device node
>>   directly?
>
>
> I don't really understand what you are trying to say.<snip>
>

Actually I think I understand what you mean now. Yes, the user can
always access a subdev's control directly from its /dev/v4l-subdevXX.
I'm only providing this feature as a convenience to the user, so that
all controls in a pipeline can be accessed from one place, i.e. the
main capture device node.

Steve