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

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Date:	Wed, 13 May 2015 15:23:01 +0300
From:	Purcareata Bogdan <b43198@...escale.com>
To:	Bogdan Purcareata <bogdan.purcareata@...escale.com>,
	<linuxppc-dev@...ts.ozlabs.org>, <scottwood@...escale.com>,
	<segher@...nel.crashing.org>, <benh@...nel.crashing.org>
CC:	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] powerpc/mpic: Remove WHOAMI readback after EOI

Ping?

On 24.03.2015 12:43, Bogdan Purcareata wrote:
> 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));
>   }
>
>   /*
>
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