From mboxrd@z Thu Jan  1 00:00:00 1970
From: Jamie Iles <jamie@jamieiles.com>
Subject: Re: [PATCHv2 02/10] ARM: vic: MULTI_IRQ_HANDLER handler
Date: Wed, 28 Sep 2011 13:08:32 +0100
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To: Linus Walleij <linus.walleij@linaro.org>
Cc: kgene.kim@samsung.com, linux@arm.linux.org.uk, linus.walleij@stericsson.com, devicetree-discuss@lists.ozlabs.org, rob.herring@calxeda.com, hsweeten@visionengravers.com, rajeev-dlh.kumar@st.com, ben-linux@fluff.org, STEricsson_nomadik_linux@list.st.com, Jamie Iles <jamie@jamieiles.com>, rubini@unipv.it, linux-arm-kernel@lists.infradead.org, rmallon@gmail.com
List-Id: devicetree@vger.kernel.org

Hi Linus,

On Wed, Sep 28, 2011 at 01:09:48PM +0200, Linus Walleij wrote:
> On Wed, Sep 28, 2011 at 12:41 PM, Jamie Iles <jamie@jamieiles.com> wrote:
> =

> > +static void vic_single_handle_irq(struct vic_device *vic, struct pt_re=
gs *regs)
> > +{
> > + =A0 =A0 =A0 u32 stat, irq;
> > + =A0 =A0 =A0 bool handled =3D false;
> > +
> > + =A0 =A0 =A0 while (!handled) {
> > + =A0 =A0 =A0 =A0 =A0 =A0 =A0 stat =3D readl_relaxed(vic->base + VIC_IR=
Q_STATUS);
> > + =A0 =A0 =A0 =A0 =A0 =A0 =A0 if (!stat)
> > + =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 break;
> > +
> > + =A0 =A0 =A0 =A0 =A0 =A0 =A0 while (stat) {
> > + =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 irq =3D fls(stat) - 1;
> =

> Isn't fls "find last set"?
> =

> That means IRQs with higher numbers will be handled first will it not?
> =

> For U300 IRQs with lower numbers will be handled first
> by iteratively testing bit 0 and shifting right:
> =

> -1002:  tst     \irqstat, #1
> -       bne     1003f
> -       add     \irqnr, \irqnr, #1
> -       movs    \irqstat, \irqstat, lsr #1
> -       bne     1002b
> =

> So I would use ffs() for this to work the same way as before in
> U300.
> =

> Since this can have some performance impact, if the platforms differ
> in whether they handle IRQs from low to high or from high to low
> might need to be a flag passed in to vic_init() or so...

I don't know how important the ordering is, but if it is important then =

we could have vic_handle_irq_msb_first() and vic_handle_irq_lsb_first() =

as the handlers so there isn't any additional indirection/selection in =

the interrupt hot-path.

Jamie