question on memory barrier

[moreau francis]

Hi,

I'm currently trying to write a USB driver for Linux. The device must be
configured by writing some values into the same register but I want to be
sure that the writing order is respected by either the compiler and the cpu.

For example, here is a bit of driver's code:

"""
#include <asm/io.h>

static inline void dev_out(u32 *reg, u32 value)
{
        writel(value, regs);
}

void config_dev(void)
{
        dev_out(reg_a, 0x0); /* first io */
        dev_out(reg_a, 0xA); /* second io */
}

void config_dev_fixed(void)
{
        dev_out(reg_a, 0x0); /* first io */
        wmb();
        dev_out(reg_a, 0xA); /* second io */
        wmb();
}
"""

In this case, am I sure that the order will be respected ? can gcc remove
the first io while optimizing...If so, does "config_dev_fixed" fix it ?

thanks for your answers,

            Francis


	

	
		
___________________________________________________________________________ 
Appel audio GRATUIT partout dans le monde avec le nouveau Yahoo! Messenger 
Téléchargez cette version sur http://fr.messenger.yahoo.com
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/