Date:   Mon, 20 Mar 2017 16:57:54 +0100
From:   Hans Verkuil <hverkuil@...all.nl>
To:     Russell King - ARM Linux <linux@...linux.org.uk>
Cc:     Steve Longerbeam <slongerbeam@...il.com>,
        Steve Longerbeam <steve_longerbeam@...tor.com>,
        robh+dt@...nel.org, mark.rutland@....com, shawnguo@...nel.org,
        kernel@...gutronix.de, fabio.estevam@....com, mchehab@...nel.org,
        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
Subject: Re: [PATCH v5 00/39] i.MX Media Driver

On 03/20/2017 03:11 PM, Russell King - ARM Linux wrote:
> On Mon, Mar 20, 2017 at 02:57:03PM +0100, Hans Verkuil wrote:
>> On 03/20/2017 02:29 PM, Russell King - ARM Linux wrote:
>>> It's what I have - remember, not everyone is happy to constantly replace
>>> their distro packages with random new stuff.
>>
>> This is a compliance test, which is continuously developed in tandem with
>> new kernel versions. If you are working with an upstream kernel, then you
>> should also use the corresponding v4l2-compliance test. What's the point
>> of using an old one?
>>
>> I will not support driver developers that use an old version of the
>> compliance test, that's a waste of my time.
> 
> The reason that people may _not_ wish to constantly update v4l-utils
> is that it changes the libraries installed on their systems.
> 
> So, the solution to that is not to complain about developers not using
> the latest version, but instead to de-couple it from the rest of the
> package, and provide it as a separate, stand-alone package that doesn't
> come with all the extra baggage.
> 
> Now, there's two possible answers to that:
> 
> 1. it depends on the libv4l2 version.  If that's so, then you are
>    insisting that people constantly move to the latest libv4l2 because
>    of API changes, and those API changes may upset applications they're
>    using.  So this isn't really on.
> 
> 2. it doesn't depend on libv4l2 version, in which case there's no reason
>    for it to be packaged with v4l-utils.

Run configure with --disable-v4l2-compliance-libv4l.

This avoids linking with libv4l and allows you to build it stand-alone.

Perhaps I should invert this option since in most cases you don't want to
run v4l2-compliance with libv4l (it's off by default unless you pass the
-w option to v4l2-compliance).

> 
> The reality is that v4l2-compliance links with libv4l2, so I'm not sure
> which it is.  What I am sure of is that I don't want to upgrade libv4l2
> on an ad-hoc basis, potentially causing issues with applications.
> 
>>>> To test actual streaming you need to provide the -s option.
>>>>
>>>> Note: v4l2-compliance has been developed for 'regular' video devices,
>>>> not MC devices. It may or may not work with the -s option.
>>>
>>> Right, and it exists to verify that the establised v4l2 API is correctly
>>> implemented.  If the v4l2 API is being offered to user applications,
>>> then it must be conformant, otherwise it's not offering the v4l2 API.
>>> (That's very much a definition statement in itself.)
>>>
>>> So, are we really going to say MC devices do not offer the v4l2 API to
>>> userspace, but something that might work?  We've already seen today
>>> one user say that they're not going to use mainline because of the
>>> crud surrounding MC.
>>>
>>
>> Actually, my understanding was that he was stuck on the old kernel code.
> 
> Err, sorry, I really don't follow.  Who is "he"?

"one user say that they're not going to use mainline because of the
crud surrounding MC."

> 
> _I_ was the one who reported the EXPBUF problem.  Your comment makes no
> sense.
> 
>> In the case of v4l2-compliance, I never had the time to make it work with
>> MC devices. Same for that matter of certain memory to memory devices.
>>
>> Just like MC devices these too behave differently. They are partially
>> supported in v4l2-compliance, but not fully.
> 
> It seems you saying that the API provided by /dev/video* for a MC device
> breaks the v4l2-compliance tests?

There may be tests in the compliance suite that do not apply for MC devices
and for which I never check. The compliance suite was never written with MC
devices in mind, and it certainly hasn't been tested much with such devices.

It's only very recent that I even got hardware that has MC support...

>From what I can tell from the feedback I got it seems to be OKish, but I
just can't guarantee that the compliance utility is correct for such devices.

In particular I doubt the streaming tests (-s, -f, etc.) will work. The -s
test *might* work if the pipeline is configured correctly before running
v4l2-compliance. I can't imagine that the -f option would work at all since
I would expect pipeline validation errors.

I've been gently pushing Helen Koike to finish her virtual MC driver
(https://patchwork.kernel.org/patch/9312783/) since having a virtual driver
makes writing compliance tests much easier.

> _No one_ has mentioned using v4l2-compliance on the subdevs.
> 
>> Complaining about this really won't help. We know it's a problem and unless
>> someone (me perhaps?) manages to get paid to work on this it's unlikely to
>> change for now.
> 
> Like the above comment, your comment makes no sense.  I'm not complaining,
> I'm trying to find out the details.

Must be me then, it did feel like complaining...

> Yes, MC stuff sucks big time right now, the documentation is poor, there's
> a lack of understanding on all sides of the issues (which can be seen by
> the different opinions that people hold.)  The only way to resolve these
> differences is via discussion, and if you're going to start thinking that
> everyone is complaining, then there's not going to be any forward progress.
> 

Regards,

	Hans

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