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

[Russell King - ARM Linux <linux@arm.linux.org.uk>]

On Wed, Jun 04, 2008 at 01:00:19PM +0200, 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).

or even interrupts.

> Shouldn't GPIO access be protected against concurrent access here?

Definitely.  It's certainly buggy as currently stands.