linux-kernel - Re: [PATCH RFT] irqchip: sun4i: Remove wrong irq

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Message-ID: <20130724095145.GK10389@lukather>
Date:	Wed, 24 Jul 2013 11:51:45 +0200
From:	Maxime Ripard <maxime.ripard@...e-electrons.com>
To:	Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:	Axel Lin <axel.lin@...ics.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH RFT] irqchip: sun4i: Remove wrong irq_ack callback
 implementation

Hi Geert,

On Fri, Jul 19, 2013 at 11:29:30AM +0200, Geert Uytterhoeven wrote:
> On Thu, Jul 11, 2013 at 6:13 PM, Maxime Ripard
> <maxime.ripard@...e-electrons.com> wrote:
> > On Sat, Jul 06, 2013 at 10:35:29PM +0800, Axel Lin wrote:
> >> According to the datasheet[1], the Interrupt IRQ Pending Registers are
> >> read-only. The implementation of sun4i_irq_ack() looks wrong because it writes
> >> to these read-only registers.
> >
> > Right, but the datasheet also says that these registers are "clear"
> > register, which might indicate that it's actually R/W.
> 
> I guess it means that the flags are cleared automatically on read?
> That's not so uncommon for interrupt pending registers.

My understanding in this case is that the pending register is just a
"copy" of the pending bits in the related hardware IP, so that clearing
it in the interrupt controller won't do much, since it will be re-set
just after the clear, while if you do clear the interrupt bit in the IP,
it will clear it automatically in the interrupt controller.

Maxime

-- 
Maxime Ripard, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com

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