From: holger.brunck@keymile•com (Holger Brunck)
To: linux-arm-kernel@lists•infradead.org
Subject: [PATCH] arm/orion: use set_bit and clear_bit in gpio implementation
Date: Wed, 07 Dec 2011 16:59:07 +0100 [thread overview]
Message-ID: <4EDF8D4B.3020806@keymile.com> (raw)
In-Reply-To: <alpine.LFD.2.02.1112071031470.2907@xanadu.home>
On 12/07/2011 04:46 PM, Nicolas Pitre wrote:
> On Wed, 7 Dec 2011, Holger Brunck wrote:
>
>> set_bit and clear_bit are already atomic operations. So use this
>> functions to set or unset gpio configurations. This makes the
>> additional spinlock unneeded.
>>
>> Signed-off-by: Stefan Bigler <stefan.bigler@keymile•com>
>> Signed-off-by: Holger Brunck <holger.brunck@keymile•com>
>> cc: Lennert Buytenhek <kernel@wantstofly•org>
>> cc: Nicolas Pitre <nico@fluxnic•net>
>> cc: Russell King <linux@arm•linux.org.uk>
>> cc: Thomas Gleixner <tglx@linutronix•de>
>
> NAK.
>
> Although this ends up equivalent in practice at the moment, the IO space
> accessed through readl() and writel() is conceptually a different thing
> than normal memory where the atomic set/clear bit functions are used.
> There is no guarantee that the value passed to readl()/writel() will
> always match the virtual address where the access is performed.
>
> Furthermore, there is no guarantee made by the atomic bit manipulation
> routines about the actual access to memory. At one point those used to
> be implemented with byte accesses not word accesses, and there is
> nothing preventing the implementation from changing in similar ways in
> the future that might have unwanted effects with IO memory.
>
> And if using an ARMv6+ core as found in the Marvell Dove or MV78xx0 SOCs
> which this patch also affects then the atomic bitops are implemented in
> terms of the load/store exclusive instructions which are architecturally
> not defined when applied to IO space.
>
Ok, thanks for the explanation.
Best regards
Holger Brunck
prev parent reply other threads:[~2011-12-07 15:59 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-12-07 14:34 [PATCH] arm/orion: use set_bit and clear_bit in gpio implementation Holger Brunck
2011-12-07 14:36 ` Lennert Buytenhek
2011-12-07 15:46 ` Nicolas Pitre
2011-12-07 15:59 ` Holger Brunck [this message]
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