[ARM] Fix FIQ issue with ARM926

Jon Eibertzon writes:
> We have noticed that the I-cache is disabled while waiting for
> interrupt in cpu_arm926_do_idle in arch/arm/mm/proc-arm926.S
> and we are curious to know why, because this causes us a great
> performance hit when executing in FIQ-handlers. Is it assumed
> here that every individual FIQ-handler re-enables the I-cache?

The I-cache disable is an errata workaround, so the solution is to
disable FIQs across the section with the I-cache disabled.

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

diff --git a/arch/arm/mm/proc-arm926.S b/arch/arm/mm/proc-arm926.S
index 5b80b6b..194ef48 100644 (file)
--- a/arch/arm/mm/proc-arm926.S
+++ b/arch/arm/mm/proc-arm926.S
@@ -105,9 +105,13 @@ ENTRY(cpu_arm926_do_idle)
        mrc     p15, 0, r1, c1, c0, 0           @ Read control register
        mcr     p15, 0, r0, c7, c10, 4          @ Drain write buffer
        bic     r2, r1, #1 << 12
+       mrs     r3, cpsr                        @ Disable FIQs while Icache
+       orr     ip, r3, #PSR_F_BIT              @ is disabled
+       msr     cpsr_c, ip
        mcr     p15, 0, r2, c1, c0, 0           @ Disable I cache
        mcr     p15, 0, r0, c7, c0, 4           @ Wait for interrupt
        mcr     p15, 0, r1, c1, c0, 0           @ Restore ICache enable
+       msr     cpsr_c, r3                      @ Restore FIQ state
        mov     pc, lr
 
 /*