Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
MIME-Version: 1.0
References: <CAK7LNASyzmYjjBkFxRc06rqf36-en-bvJvrKcg6iiRfjoPCxhQ@mail.gmail.com>
 <CAK8P3a2AeUpmNfFLJSvHT=AJ0kFRT2B=TWDm0HsTwoHt2jQ0gQ@mail.gmail.com>
 <CAK7LNATPbCjwzVnAigsQ8tQRXjC31uxgPg3jgi7pwp+N1RPgWw@mail.gmail.com>
 <CAK8P3a3cURmbGZc-6ESLjrF465VLnBroD4QENyfsSsCrNenRrA@mail.gmail.com>
 <CAK7LNARN=iNmresDJ2=J1wOb2QYoZ7yw4O0Q9sYVPo0jRKDf=w@mail.gmail.com> <CAK8P3a133ekPqkLWfC2ee0mT3iLbFzSjJ9FDokSyaX+hMVigKA@mail.gmail.com>
In-Reply-To: <CAK8P3a133ekPqkLWfC2ee0mT3iLbFzSjJ9FDokSyaX+hMVigKA@mail.gmail.com>
From:   Masahiro Yamada <yamada.masahiro@socionext.com>
Date:   Sun, 21 Jul 2019 23:58:32 +0900
Message-ID: <CAK7LNATAhhmeKtQYJYEje3B26zy3EtdqegRL7YmbsDOJ=0HcAg@mail.gmail.com>
Subject: Re: [Question] orphan platform data header
To:     Arnd Bergmann <arnd@arndb.de>
Cc:     Ben Dooks <ben.dooks@codethink.co.uk>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        DTML <devicetree@vger.kernel.org>,
        linux-arm-kernel <linux-arm-kernel@lists.infradead.org>
Content-Type: text/plain; charset="UTF-8"
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Sun, Jul 21, 2019 at 11:15 PM Arnd Bergmann <arnd@arndb.de> wrote:
>
> On Sun, Jul 21, 2019 at 2:13 PM Masahiro Yamada
> <yamada.masahiro@socionext.com> wrote:
> > On Sun, Jul 21, 2019 at 6:10 PM Arnd Bergmann <arnd@arndb.de> wrote:
> > > On Sun, Jul 21, 2019 at 5:45 AM Masahiro Yamada
> > > <yamada.masahiro@socionext.com> wrote:
> > > > On Sat, Jul 20, 2019 at 10:55 PM Arnd Bergmann <arnd@arndb.de> wrote:
> > > > > On Sat, Jul 20, 2019 at 5:26 AM Masahiro Yamada <yamada.masahiro@socionext.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