linux-kernel - Re: [PATCH] ARM: Gemini: Add support for PCI BUS

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-Id: <201011291745.22566.arnd@arndb.de>
Date:	Mon, 29 Nov 2010 17:45:22 +0100
From:	Arnd Bergmann <arnd@...db.de>
To:	Paulius Zaleckas <paulius.zaleckas@...il.com>
Cc:	linux-arm-kernel@...ts.infradead.org,
	Hans Ulli Kroll <ulli.kroll@...glemail.com>,
	Russell King <linux@....linux.org.uk>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ARM: Gemini: Add support for PCI BUS

On Monday 29 November 2010, Paulius Zaleckas wrote:
> > The I/O ordering is probably not what you think it is.
> > There is no ordering guarantee between __raw_writel and
> > spin_lock/spin_unlock, so you really should be using
> > readl/writel.
> 
> No he really should NOT use readl/writel. The ONLY difference
> between readl/writel and __raw_readl/__raw_writel is endianess
> conversion. __raw_*l is not doing it. Which to use depend only
> on HW.

There are many differences between readl and __raw_readl, including

* __raw_readl does not have barriers and does not serialize with
  spinlocks, so it breaks on out-of-order CPUs.
* __raw_readl does not have a specific endianess, while readl is
  fixed little-endian, just as the hardware is in this case.
  The endian-conversion is a NOP on little-endian ARM, but required
  if you actually run on a big-endian ARM (you don't).
* __raw_readl may not be atomic, gcc is free to split the access
  into byte wise reads (it normally does not, unless you mark
  the pointer __attribute__((packed))).

In essence, it is almost never a good idea to use __raw_readl, and
the double underscores should tell you so.

	Arnd
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/