linux-kernel - Re: [PATCH v2 3/3] irqchip: orion: reverse irq handling priority

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Date:	Sun, 4 May 2014 20:10:22 -0400
From:	Jason Cooper <jason@...edaemon.net>
To:	Sebastian Hesselbarth <sebastian.hesselbarth@...il.com>
Cc:	Andrew Lunn <andrew@...n.ch>, linux-kernel@...r.kernel.org,
	Gregory Clement <gregory.clement@...e-electrons.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v2 3/3] irqchip: orion: reverse irq handling priority

On Mon, Apr 28, 2014 at 11:12:08PM +0200, Sebastian Hesselbarth wrote:
> Non-DT irq handlers were working through irq causes from most-significant
> to least-significant bit, while DT irqchip driver does it the other way
> round. This revealed some more HW issues on Kirkwood peripheral IP, where
> spurious sdio irqs can happen although irqs are masked.
> 
> Also, the generated binaries show that original non-DT order compared
> to DT order save two instructions for each bit count check:
> 
> irqchip DT order with ffs():
>   60:   e3a06001        mov     r6, #1
>   64:   e2643000        rsb     r3, r4, #0
>   68:   e0033004        and     r3, r3, r4
>   6c:   e16f3f13        clz     r3, r3
>   70:   e263301f        rsb     r3, r3, #31
>   74:   e1c44316        bic     r4, r4, r6, lsl r3
>   78:   e5971004        ldr     r1, [r7, #4]
> 
> Original non-DT order with fls():
>   60:   e3a07001        mov     r7, #1
>   64:   e16f3f14        clz     r3, r4
>   68:   e263301f        rsb     r3, r3, #31
>   6c:   e1c44317        bic     r4, r4, r7, lsl r3
>   70:   e5951004        ldr     r1, [r5, #4]
> 
> Therefore, reverse irq bit handling back to original order by replacing
> ffs() with fls().
> 
> Signed-off-by: Sebastian Hesselbarth <sebastian.hesselbarth@...il.com>
> Acked-by: Jason Cooper <jason@...edaemon.net>
> ---
> Changelog:
> v1->v2:
> - reword commit msg to state less number of instructions
> 
> Cc: Jason Cooper <jason@...edaemon.net>
> Cc: Andrew Lunn <andrew@...n.ch>
> Cc: Gregory Clement <gregory.clement@...e-electrons.com>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: linux-arm-kernel@...ts.infradead.org
> Cc: linux-kernel@...r.kernel.org
> ---
>  drivers/irqchip/irq-orion.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)

Applied to mvebu/irqchip for routing through the tip tree.  Tweaked
capitalization of subject line to match the other commits in that
directory.

thx,

Jason.
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