linux-kernel - Re: Locking in the (now generic) GPIO infrastructure?

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Message-ID: <18506.30304.646369.956267@alkaid.it.uu.se>
Date:	Sat, 7 Jun 2008 13:52:00 +0200
From:	Mikael Pettersson <mikpe@...uu.se>
To:	David Brownell <david-b@...bell.net>
Cc:	"Leon Woestenberg" <leon.woestenberg@...il.com>,
	LAK <linux-arm-kernel@...ts.arm.linux.org.uk>,
	"Linux Kernel list" <linux-kernel@...r.kernel.org>
Subject: Re: Locking in the (now generic) GPIO infrastructure?

David Brownell writes:
 > On Wednesday 04 June 2008, Leon Woestenberg wrote:
 > > include/asm-arm/arch-ixp4xx/platform.h:
 > > static inline void gpio_line_set(u8 line, int value)
 > > {
 > >         if (value == IXP4XX_GPIO_HIGH)
 > >             *IXP4XX_GPIO_GPOUTR |= (1 << line);
 > >         else if (value == IXP4XX_GPIO_LOW)
 > >             *IXP4XX_GPIO_GPOUTR &= ~(1 << line);
 > > }
 > > 
 > > Under a Linux kernel where multiple drivers are accessing GPIO, the
 > > latter does not seem safe against preemption (assuming the memory
 > > read-modify-write is not atomic).
 > > 
 > > Shouldn't GPIO access be protected against concurrent access here?
 > 
 > Well, against an IRQ in the middle of those read/modify/write
 > sequences hidden by the "|=" and "&=" syntax.  Last I knew,
 > no XScale CPUs support on-chip SMP.

The IOP342 has two XScale cores on-chip. However, these cores are
still only ARMv5TE and Linux wants ARMv6 or newer for SMP, so I
don't know to what extent the IOP342 is supported by Linux.
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