linux-kernel - RE: [PATCH] media: v4l2-compat-ioctl32.c: copy reserved2 field in get_v4l2

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Date:   Mon, 20 Apr 2020 09:40:33 +0900
From:   "Sunyoung Kang" <sy0816.kang@...sung.com>
To:     "'Greg Kroah-Hartman'" <gregkh@...uxfoundation.org>
Cc:     <mchehab@...nel.org>, "'Hans Verkuil'" <hverkuil-cisco@...all.nl>,
        "'Arnd Bergmann'" <arnd@...db.de>,
        "'Thomas Gleixner'" <tglx@...utronix.de>,
        <linux-media@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH] media: v4l2-compat-ioctl32.c: copy reserved2 field in
 get_v4l2_buffer32

I understand what you mean.
However, the way to transmit information about the buffer is only flags in
v4l2_buffer
In flags in v4l2_buffer, there is no reserved bit field that can be used for
custom.
Additional information about the buffer is needed to provide various
functions required by the customers but flags is not enough. So reserved2 is
used as an alternative.
Can you suggest a better opinion?

And copy the reserved2 value in put_v4l2_buffer32(), but it is missing only
in get_v4l2_buffer32().
Can't I put it in get_v4l2_buffer32()?

Thanks,
Sunyoung

> -----Original Message-----
> From: 'Greg Kroah-Hartman' <gregkh@...uxfoundation.org>
> Sent: Saturday, April 18, 2020 4:37 PM
> To: Sunyoung Kang <sy0816.kang@...sung.com>
> Cc: mchehab@...nel.org; 'Hans Verkuil' <hverkuil-cisco@...all.nl>; 'Arnd
> Bergmann' <arnd@...db.de>; 'Thomas Gleixner' <tglx@...utronix.de>; linux-
> media@...r.kernel.org; linux-kernel@...r.kernel.org
> Subject: Re: [PATCH] media: v4l2-compat-ioctl32.c: copy reserved2 field in
> get_v4l2_buffer32
> 
> On Sat, Apr 18, 2020 at 12:14:09PM +0900, Sunyoung Kang wrote:
> > Exynos video codec driver uses reserved2 value. How will reserved2 be
> > used for future use?
> 
> No driver should be using the "reserved" fields, as they are "reserved"
> by the api for future expansion of it.  They are not driver-specific
> fields to be used that way at all.
> 
> thanks,
> 
> greg k-h