[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 <redacted>
---
 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

Ping?

On 24.03.2015 12:43, Bogdan Purcareata wrote:

On Wed, 2015-05-13 at 15:23 +0300, Purcareata Bogdan wrote:

Ping?

On 24.03.2015 12:43, Bogdan Purcareata wrote:

quoted

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 <redacted>
---
  arch/powerpc/sysdev/mpic.c | 1 -
  1 file changed, 1 deletion(-)

Don't top-post.

This is commit 56302c53d3dc477b8360954fc92c1dfc4fc0ec54 in Linus's tree.

-Scott