linux-kernel - Re: [PATCH v2 7/9] [media] v4l2: introduce v4l2

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Date:	Fri, 18 Sep 2015 11:52:28 +0200
From:	Hans Verkuil <hverkuil@...all.nl>
To:	Arnd Bergmann <arnd@...db.de>
CC:	linux-media@...r.kernel.org, linux-kernel@...r.kernel.org,
	y2038@...ts.linaro.org,
	Mauro Carvalho Chehab <mchehab@....samsung.com>,
	linux-api@...r.kernel.org, linux-samsung-soc@...r.kernel.org
Subject: Re: [PATCH v2 7/9] [media] v4l2: introduce v4l2_timeval

On 09/18/15 11:43, Arnd Bergmann wrote:
> On Friday 18 September 2015 11:27:40 Hans Verkuil wrote:
>> Ah, OK. Got it.
>>
>> I think this is dependent on the upcoming media workshop next month. If we
>> decide to redesign v4l2_buffer anyway, then we can avoid timeval completely.
>> And the only place where we would need to convert it in the compat code
>> hidden in the v4l2 core (likely v4l2-ioctl.c).
> 
> Ah, I think I understood the idea now, I missed that earlier when you mention
> the idea.
> 
> So what you are saying here is that you could come up with a new unambiguous
> (using only __u32 and __u64 types and no pointers) format that gets exposed
> to a new set of ioctls, and then change the handling of the existing three
> formats (native 64-bit, traditional 32-bit, and 32-bit with 64-bit time_t)
> so they get converted into the new format by the common ioctl handling code?

Right. Drivers only see the new struct, and only v4l2-ioctl.c (and possible
v4l2-compat-ioctl32.c) see the old ones.

BTW, I will probably pick up patches 4 and 6 for 4.4. That should help a bit.

Regards,

	Hans

>> I am not really keen on having v4l2_timeval in all these drivers. I would
>> have to check them anyway since I suspect that in several drivers the local
>> timeval variable can be avoided by rewriting that part of the driver.
> 
> I've tried to do that for all the drivers where I could find an easy solution
> in patch 6/9, but I'm sure you can do it for a couple more.
> 
> We could also do a lightweight redesign and use 'timespec64' internally
> in all the drivers and then convert that to 'timeval' or the 64-bit
> format of that in the ioctl handler. This is also something I tried at
> some point but then found it a bit more intuitive to leave the normal ioctl
> path alone and have an explicit type.
> 
>> Personally I am in favor of a redesigned v4l2_buffer: it's awkward to use
>> with multiplanar formats, there is cruft in there that can be removed (timecode),
>> and there is little space for additions (HW-specific timecodes, more buffer
>> meta data, etc).
>>
>> We'll see.
> 
> Ok.
> 
> 	Arnd
> 
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