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

From	Hans Verkuil <hverkuil@xs4all.nl>
Newsgroups	linux.kernel
Subject	Re: [PATCH v4 14/36] [media] v4l2-mc: add a function to inherit controls from a pipeline
Date	2017-03-20 12:20 +0100
Message-ID	<tn3vY-3VF-9@gated-at.bofh.it> (permalink)
References	(7 earlier) <tkxAd-ys-13@gated-at.bofh.it> <tkLDb-2Dk-9@gated-at.bofh.it> <tkPx8-5ja-19@gated-at.bofh.it> <tlYyl-5OT-7@gated-at.bofh.it> <tlYI1-5S8-7@gated-at.bofh.it>
Organization	linux.* mail to news gateway

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On 03/17/2017 12:55 PM, Sakari Ailus wrote:
> Hi Russell,
> 
> On 03/17/17 13:42, Russell King - ARM Linux wrote:
>> On Tue, Mar 14, 2017 at 08:55:36AM +0100, Hans Verkuil wrote:
>>> We're all very driver-development-driven, and userspace gets very little
>>> attention in general. So before just throwing in the towel we should take
>>> a good look at the reasons why there has been little or no development: is
>>> it because of fundamental design defects, or because nobody paid attention
>>> to it?
>>>
>>> I strongly suspect it is the latter.
>>>
>>> In addition, I suspect end-users of these complex devices don't really care
>>> about a plugin: they want full control and won't typically use generic
>>> applications. If they would need support for that, we'd have seen much more
>>> interest. The main reason for having a plugin is to simplify testing and
>>> if this is going to be used on cheap hobbyist devkits.
>>
>> I think you're looking at it with a programmers hat on, not a users hat.
>>
>> Are you really telling me that requiring users to 'su' to root, and then
>> use media-ctl to manually configure the capture device is what most
>> users "want" ?
> 
> It depends on who the user is. I don't think anyone is suggesting a
> regular end user is the user of all these APIs: it is either an
> application tailored for that given device, a skilled user with his test
> scripts or as suggested previously, a libv4l plugin knowing the device
> or a generic library geared towards providing best effort service. The
> last one of this list does not exist yet and the second last item
> requires help.
> 
> Typically this class of devices is simply not up to provide the level of
> service you're requesting without additional user space control library
> which is responsible for automatic white balance, exposure and focus.
> 
> Making use of the full potential of the hardware requires using a more
> expressive interface. That's what the kernel interface must provide. If
> we decide to limit ourselves to a small sub-set of that potential on the
> level of the kernel interface, we have made a wrong decision. It's as
> simple as that. This is why the functionality (and which requires taking
> a lot of policy decisions) belongs to the user space. We cannot have
> multiple drivers providing multiple kernel interfaces for the same hardware.

Right. With my Cisco hat on I can tell you that Cisco would want full low-level
control. If the driver would limit us we would not be able to use it.

Same with anyone who wants to put Android CameraHAL on top of a V4L2 driver:
they would need full control. Some simplified interface would be unacceptable.

> 
> That said, I'm not trying to provide an excuse for not having libraries
> available to help the user to configure and control the device more or
> less automatically even in terms of best effort. It's something that
> does require attention, a lot more of it than it has received in recent
> few years.

Right.

Regards,

	Hans

Thread

Re: [PATCH v4 14/36] [media] v4l2-mc: add a function to inherit  controls from a pipeline Mauro Carvalho Chehab <mchehab@s-opensource.com> - 2017-03-14 04:50 +0100
  Re: [PATCH v4 14/36] [media] v4l2-mc: add a function to inherit  controls from a pipeline Hans Verkuil <hverkuil@xs4all.nl> - 2017-03-14 09:00 +0100
    Re: [PATCH v4 14/36] [media] v4l2-mc: add a function to inherit  controls from a pipeline Mauro Carvalho Chehab <mchehab@s-opensource.com> - 2017-03-14 11:30 +0100
      media / v4l2-mc: wishlist for complex cameras (was Re: [PATCH v4  14/36] [media] v4l2-mc: add a function to inherit controls from a pipeline) Pavel Machek <pavel@ucw.cz> - 2017-03-14 23:40 +0100
        Re: media / v4l2-mc: wishlist for complex cameras (was Re: [PATCH  v4 14/36] [media] v4l2-mc: add a function to inherit controls from a  pipeline) Mauro Carvalho Chehab <mchehab@s-opensource.com> - 2017-03-15 02:00 +0100
          Re: media / v4l2-mc: wishlist for complex cameras (was Re: [PATCH         v4 14/36] [media] v4l2-mc: add a function to inherit controls from         a pipeline) Philippe De Muyter <phdm@macq.eu> - 2017-03-15 12:10 +0100
            Re: media / v4l2-mc: wishlist for complex cameras (was Re: [PATCH  v4 14/36] [media] v4l2-mc: add a function to inherit controls from a  pipeline) Nicolas Dufresne <nicolas@ndufresne.ca> - 2017-03-15 20:00 +0100
              Re: media / v4l2-mc: wishlist for complex cameras (was Re: [PATCH  v4 14/36] [media] v4l2-mc: add a function to inherit controls from a  pipeline) Philipp Zabel <p.zabel@pengutronix.de> - 2017-03-16 10:30 +0100
                Re: media / v4l2-mc: wishlist for complex cameras (was Re: [PATCH         v4 14/36] [media] v4l2-mc: add a function to inherit controls from         a pipeline) Philippe De Muyter <phdm@macq.eu> - 2017-03-16 11:00 +0100
                Re: media / v4l2-mc: wishlist for complex cameras (was Re: [PATCH  v4 14/36] [media] v4l2-mc: add a function to inherit controls from a  pipeline) Philipp Zabel <p.zabel@pengutronix.de> - 2017-03-16 11:10 +0100
                Re: media / v4l2-mc: wishlist for complex cameras (was Re: [PATCH         v4 14/36] [media] v4l2-mc: add a function to inherit controls from         a pipeline) Philippe De Muyter <phdm@macq.eu> - 2017-03-16 11:30 +0100
          Re: media / v4l2-mc: wishlist for complex cameras (was Re: [PATCH v4  14/36] [media] v4l2-mc: add a function to inherit controls from a pipeline) Pavel Machek <pavel@ucw.cz> - 2017-03-15 19:10 +0100
            Re: media / v4l2-mc: wishlist for complex cameras (was Re: [PATCH  v4 14/36] [media] v4l2-mc: add a function to inherit controls from a  pipeline) Mauro Carvalho Chehab <mchehab@s-opensource.com> - 2017-03-15 21:30 +0100
              Re: media / v4l2-mc: wishlist for complex cameras (was Re: [PATCH v4  14/36] [media] v4l2-mc: add a function to inherit controls from a pipeline) Pavel Machek <pavel@ucw.cz> - 2017-03-16 23:20 +0100
      Re: [PATCH v4 14/36] [media] v4l2-mc: add a function to inherit  controls from a pipeline Hans Verkuil <hverkuil@xs4all.nl> - 2017-03-20 14:30 +0100
        Re: [PATCH v4 14/36] [media] v4l2-mc: add a function to inherit  controls from a pipeline Mauro Carvalho Chehab <mchehab@s-opensource.com> - 2017-03-20 16:50 +0100
          Re: [PATCH v4 14/36] [media] v4l2-mc: add a function to inherit  controls from a pipeline Russell King - ARM Linux <linux@armlinux.org.uk> - 2017-03-20 17:20 +0100
            Re: [PATCH v4 14/36] [media] v4l2-mc: add a function to inherit  controls from a pipeline Mauro Carvalho Chehab <mchehab@s-opensource.com> - 2017-03-20 18:40 +0100
    Re: [PATCH v4 14/36] [media] v4l2-mc: add a function to inherit  controls from a pipeline Russell King - ARM Linux <linux@armlinux.org.uk> - 2017-03-17 12:50 +0100
      Re: [PATCH v4 14/36] [media] v4l2-mc: add a function to inherit  controls from a pipeline Sakari Ailus <sakari.ailus@linux.intel.com> - 2017-03-17 13:00 +0100
        Re: [PATCH v4 14/36] [media] v4l2-mc: add a function to inherit  controls from a pipeline Philipp Zabel <p.zabel@pengutronix.de> - 2017-03-17 15:00 +0100
          Re: [PATCH v4 14/36] [media] v4l2-mc: add a function to inherit  controls from a pipeline Russell King - ARM Linux <linux@armlinux.org.uk> - 2017-03-17 15:50 +0100
            Re: [PATCH v4 14/36] [media] v4l2-mc: add a function to inherit  controls from a pipeline Hans Verkuil <hverkuil@xs4all.nl> - 2017-03-20 14:20 +0100
              Re: [PATCH v4 14/36] [media] v4l2-mc: add a function to inherit  controls from a pipeline Mauro Carvalho Chehab <mchehab@s-opensource.com> - 2017-03-20 16:20 +0100
        Re: [PATCH v4 14/36] [media] v4l2-mc: add a function to inherit  controls from a pipeline Mauro Carvalho Chehab <mchehab@s-opensource.com> - 2017-03-17 15:10 +0100
          Re: [PATCH v4 14/36] [media] v4l2-mc: add a function to inherit  controls from a pipeline Pavel Machek <pavel@ucw.cz> - 2017-03-21 12:20 +0100
        Re: [PATCH v4 14/36] [media] v4l2-mc: add a function to inherit  controls from a pipeline Hans Verkuil <hverkuil@xs4all.nl> - 2017-03-20 12:20 +0100
      Re: [PATCH v4 14/36] [media] v4l2-mc: add a function to inherit  controls from a pipeline Philipp Zabel <p.zabel@pengutronix.de> - 2017-03-17 13:10 +0100
        Re: [PATCH v4 14/36] [media] v4l2-mc: add a function to inherit  controls from a pipeline Russell King - ARM Linux <linux@armlinux.org.uk> - 2017-03-17 13:30 +0100
          Re: [PATCH v4 14/36] [media] v4l2-mc: add a function to inherit  controls from a pipeline Mauro Carvalho Chehab <mchehab@s-opensource.com> - 2017-03-17 19:00 +0100
      Re: [PATCH v4 14/36] [media] v4l2-mc: add a function to inherit  controls from a pipeline Pavel Machek <pavel@ucw.cz> - 2017-03-19 14:30 +0100
    Re: [PATCH v4 14/36] [media] v4l2-mc: add a function to inherit controls from a pipeline Laurent Pinchart <laurent.pinchart@ideasonboard.com> - 2017-03-26 18:50 +0200

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