linux-kernel - Re: [Question] orphan platform data header

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Message-ID: <CAK7LNATAhhmeKtQYJYEje3B26zy3EtdqegRL7YmbsDOJ=0HcAg@mail.gmail.com>
Date:   Sun, 21 Jul 2019 23:58:32 +0900
From:   Masahiro Yamada <yamada.masahiro@...ionext.com>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Ben Dooks <ben.dooks@...ethink.co.uk>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        DTML <devicetree@...r.kernel.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [Question] orphan platform data header

On Sun, Jul 21, 2019 at 11:15 PM Arnd Bergmann <arnd@...db.de> wrote:
>
> On Sun, Jul 21, 2019 at 2:13 PM Masahiro Yamada
> <yamada.masahiro@...ionext.com> wrote:
> > On Sun, Jul 21, 2019 at 6:10 PM Arnd Bergmann <arnd@...db.de> wrote:
> > > On Sun, Jul 21, 2019 at 5:45 AM Masahiro Yamada
> > > <yamada.masahiro@...ionext.com> wrote:
> > > > On Sat, Jul 20, 2019 at 10:55 PM Arnd Bergmann <arnd@...db.de> wrote:
> > > > > On Sat, Jul 20, 2019 at 5:26 AM Masahiro Yamada <yamada.masahiro@...ionext.com> wrote:
> >
> >
> > Another example that I have no idea
> > how it works:
> >
> > drivers/net/hamradio/yam.c
> >
> > yam_ioctl() reads data from user-space,
> > but the data structures for ioctl are
> > defined in include/linux/yam.h
>
> That is different: the hardware attaches to a serial port and may well
> be usable, and the user space side just contains a copy of the header,
> see https://github.com/nwdigitalradio/ax25-tools/tree/master/yamdrv

Oh, I did not know that
user-space had a copy of that.


> > If we want to fix this, we could move it
> > to include/uapi/linux/yam.h
>
> We could do that, or just leave it alone, as nobody would
> tell the difference.

When we are changing structures in uapi,
it is very likely a red alert.
On the other hand, we can change code outside of uapi
more safely.
One benefit of uapi is we can catch the compatibility level
from the directory path.


>
> > But, if nobody has reported any problem about this,
> > it might be a good proof that nobody is using this driver.
> >
> > Maybe, can we simply drop odd drivers??
>
> Both the kernel driver and the user space side have a maintainer, and
> I see no indication that it is actually broken. The driver is clearly
> a relic from old times (earlier than 2.4) and we would not merge
> this driver today.
>
> It seems more useful to keep looking for drivers with a platform_data
> header file that is no longer included by any platform for candidates
> that may be obsolete.

OK.

Thanks.




-- 
Best Regards
Masahiro Yamada