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Commit b4a1f67f authored by Lennert Buytenhek's avatar Lennert Buytenhek Committed by Russell King
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[ARM] 3053/1: introduce ixp2000_reg_wrb (ixp2000_reg_write plus readback) 



Patch from Lennert Buytenhek

Introduce ixp2000_reg_wrb, which is a variant of ixp2000_reg_write
that does a readback from the target register, to make sure that
the write has been flushed out of the write buffer.

Unlike the previous (ineffective) readback in ixp2000_reg_write, this
readback is followed by an instruction that depends on the value of
the readback so that the CPU actually stalls until the readback has
completed.

Signed-off-by: default avatarLennert Buytenhek <buytenh@wantstofly.org>
Signed-off-by: default avatarDeepak Saxena <dsaxena@plexity.net>
Signed-off-by: default avatarRussell King <rmk+kernel@arm.linux.org.uk>
parent ecbea7a2

include/asm-arm/arch-ixp2000/platform.h

+25 −0
Original line number Diff line number Diff line
@@ -25,6 +25,31 @@ static inline void ixp2000_reg_write(volatile void *reg, unsigned long val) 
	*((volatile unsigned long *)reg) = val;

}



/*

 * On the IXP2400, we can't use XCB=000 due to chip bugs.  We use

 * XCB=101 instead, but that makes all I/O accesses bufferable.  This

 * is not a problem in general, but we do have to be slightly more

 * careful because I/O writes are no longer automatically flushed out

 * of the write buffer.

 *

 * In cases where we want to make sure that a write has been flushed

 * out of the write buffer before we proceed, for example when masking

 * a device interrupt before re-enabling IRQs in CPSR, we can use this

 * function, ixp2000_reg_wrb, which performs a write, a readback, and

 * issues a dummy instruction dependent on the value of the readback

 * (mov rX, rX) to make sure that the readback has completed before we

 * continue.

 */

static inline void ixp2000_reg_wrb(volatile void *reg, unsigned long val)

{

	unsigned long dummy;



	*((volatile unsigned long *)reg) = val;



	dummy = *((volatile unsigned long *)reg);

	__asm__ __volatile__("mov %0, %0" : "+r" (dummy));

}



/*

 * Boards may multiplex different devices on the 2nd channel of 

 * the slowport interface that each need different configuration