From: David Laight <David.Laight@ACULAB.COM>
To: 'Arnd Bergmann' <arnd@kernel.org>,
Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Guenter Roeck <linux@roeck-us.net>,
Al Viro <viro@zeniv.linux.org.uk>,
Linus Torvalds <torvalds@linux-foundation.org>,
"David S. Miller" <davem@davemloft.net>,
Dmitry Torokhov <dmitry.torokhov@gmail.com>,
Christian Koenig <christian.koenig@amd.com>,
Huang Rui <ray.huang@amd.com>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
linux-sparc <sparclinux@vger.kernel.org>,
Martin Sebor <msebor@gcc.gnu.org>
Subject: RE: [PATCH] Enable '-Werror' by default for all kernel builds
Date: Wed, 8 Sep 2021 14:47:52 +0000 [thread overview]
Message-ID: <401c9db63f764389bec7faaf41deb92f@AcuMS.aculab.com> (raw)
In-Reply-To: <CAK8P3a3yJHvJaFHUh2+5GPm2n_g9gSfX2rFbrSLzDt6yC4eDog@mail.gmail.com>
From: Arnd Bergmann
> Sent: 08 September 2021 10:50
...
> > > I don't know the hardware, so I can not answer the ioremap() question.
> >
> > Yes it should. But this driver dates back to 2.1.110, when only
> > half of the architectures already had ioremap().
>
> How does mvme16x even create the mapping? Is this a virtual address
> that is hardwired to the bus or do you have a static mapping somewhere?
> I see two other drivers accessing the nvram here
>
> arch/m68k/mvme16x/config.c:static MK48T08ptr_t volatile rtc = (MK48T08ptr_t)MVME_RTC_BASE;
> arch/m68k/mvme16x/rtc.c: volatile MK48T08ptr_t rtc = (MK48T08ptr_t)MVME_RTC_BASE;
>
> The same trick should work here, just create a local variable with a
> volatile pointer and read from that.
Or define a C 'extern' for the actual data and get the linker script
to assign a fixed value to the symbol.
(Although that does pollute the global namespace.)
An alternative is to use an asm statement so the compiler
cannot track the actual value.
Something like:
#define launder(x) asm volatile( "" : "+r" (x))
MK48T08ptr_t rtc = (void *)MVME_RTC_BASE;
launder(rtc);
That also works a bit like READ_ONCE() except that is works
on a value that is (hopefully) already in a register rather
that during the read from memory.
Useful when the compiler's 'value tracking' pessimises code.
David
-
Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)
next prev parent reply other threads:[~2021-09-08 14:48 UTC|newest]
Thread overview: 50+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-09-06 14:26 [PATCH] Enable '-Werror' by default for all kernel builds Guenter Roeck
2021-09-06 16:12 ` Linus Torvalds
2021-09-06 16:18 ` Linus Torvalds
2021-09-06 17:05 ` Guenter Roeck
2021-09-06 23:06 ` Linus Torvalds
2021-09-06 23:49 ` Guenter Roeck
2021-09-07 1:12 ` Linus Torvalds
2021-09-07 2:29 ` Guenter Roeck
2021-09-07 15:50 ` Guenter Roeck
2021-09-07 8:56 ` Arnd Bergmann
2021-09-08 4:28 ` Guenter Roeck
2021-09-08 4:48 ` Al Viro
2021-09-08 5:14 ` Guenter Roeck
2021-09-08 7:11 ` Geert Uytterhoeven
2021-09-08 9:50 ` Arnd Bergmann
2021-09-08 10:10 ` Geert Uytterhoeven
2021-09-08 10:21 ` Geert Uytterhoeven
2021-09-08 12:42 ` Guenter Roeck
2021-09-08 13:19 ` Al Viro
2021-09-08 13:54 ` Guenter Roeck
2021-09-08 14:47 ` David Laight [this message]
2021-09-08 4:55 ` Linus Torvalds
2021-09-08 5:46 ` Guenter Roeck
2021-09-07 5:32 ` Huang Rui
2021-09-07 6:15 ` Christian König
2021-09-07 6:58 ` Geert Uytterhoeven
2021-09-07 2:30 ` Nathan Chancellor
2021-09-07 9:11 ` Arnd Bergmann
2021-09-07 17:10 ` Linus Torvalds
2021-09-07 17:33 ` Linus Torvalds
2021-09-07 21:07 ` Harry Wentland
2021-09-08 3:52 ` Harry Wentland
2021-09-08 4:41 ` Linus Torvalds
2021-09-09 0:48 ` Harry Wentland
2021-09-07 17:48 ` Guenter Roeck
2021-09-07 19:12 ` Nathan Chancellor
2021-09-08 20:55 ` Nathan Chancellor
2021-09-08 21:16 ` Guenter Roeck
2021-09-08 21:58 ` Marco Elver
2021-09-09 5:58 ` Christoph Hellwig
2021-09-09 6:07 ` Guenter Roeck
2021-09-09 7:30 ` Christian König
2021-09-09 14:59 ` Guenter Roeck
2021-09-09 10:53 ` Marco Elver
2021-09-09 11:00 ` Arnd Bergmann
2021-09-09 11:43 ` Marco Elver
2021-09-09 12:55 ` Arnd Bergmann
2021-09-09 16:53 ` Linus Torvalds
2021-09-09 16:46 ` Linus Torvalds
2021-09-21 15:41 ` Arnd Bergmann
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=401c9db63f764389bec7faaf41deb92f@AcuMS.aculab.com \
--to=david.laight@aculab.com \
--cc=arnd@kernel.org \
--cc=christian.koenig@amd.com \
--cc=davem@davemloft.net \
--cc=dmitry.torokhov@gmail.com \
--cc=geert@linux-m68k.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux@roeck-us.net \
--cc=msebor@gcc.gnu.org \
--cc=ray.huang@amd.com \
--cc=sparclinux@vger.kernel.org \
--cc=torvalds@linux-foundation.org \
--cc=viro@zeniv.linux.org.uk \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).