linux-kernel - [PATCH] powerpc/mpic: Remove WHOAMI readback after EOI

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Date:	Tue, 24 Mar 2015 10:43:43 +0000
From:	Bogdan Purcareata <bogdan.purcareata@...escale.com>
To:	<linuxppc-dev@...ts.ozlabs.org>, <scottwood@...escale.com>,
	<segher@...nel.crashing.org>, <benh@...nel.crashing.org>
CC:	<linux-kernel@...r.kernel.org>
Subject: [PATCH] powerpc/mpic: Remove WHOAMI readback after EOI

After previous discussions regarding the subject [1][2], there's no clear
explanation or reason why the call was needed in the first place. The sensible
argument is some sort of synchronization between the CPU and the MPIC, which
hasn't been pointed out precisely and is no longer required (at least on BookE
platforms).

The benefit of this change is saving a MMIO trap per interrupt when running in a
KVM guest.

[1] https://patchwork.ozlabs.org/patch/429098/
[2] https://patchwork.ozlabs.org/patch/433557/

Signed-off-by: Bogdan Purcareata <bogdan.purcareata@...escale.com>
---
 arch/powerpc/sysdev/mpic.c | 1 -
 1 file changed, 1 deletion(-)

diff --git a/arch/powerpc/sysdev/mpic.c b/arch/powerpc/sysdev/mpic.c
index bbfbbf2..045e72a9 100644
--- a/arch/powerpc/sysdev/mpic.c
+++ b/arch/powerpc/sysdev/mpic.c
@@ -655,7 +655,6 @@ static inline struct mpic * mpic_from_irq_data(struct irq_data *d)
 static inline void mpic_eoi(struct mpic *mpic)
 {
 	mpic_cpu_write(MPIC_INFO(CPU_EOI), 0);
-	(void)mpic_cpu_read(MPIC_INFO(CPU_WHOAMI));
 }
 
 /*
-- 
2.1.4

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