Re: [PATCH for v3.15] net: mvmdio: Check for a valid interrupt instead of an error

[Ezequiel Garcia <ezequiel.garcia@free-electrons.com>]

On Apr 29, Sebastian Hesselbarth wrote:
> On 04/29/2014 09:49 PM, Ezequiel Garcia wrote:
> > The following commit:
> > 
> > commit 9ec36cafe43bf835f8f29273597a5b0cbc8267ef
> > Author: Rob Herring <robh@kernel.org>
> > Date:   Wed Apr 23 17:57:41 2014 -0500
> > 
> >     of/irq: do irq resolution in platform_get_irq
> > 
> > changed platform_get_irq() which now returns ENODEV and EPROBE_DEFER,
> > in addition to ENXIO. If there's no interrupt for mvmdio, platform_get_irq()
> > returns ENODEV, but we currently check only for ENXIO.
> > 
> > Fix this by looking for a positive integer, which is the proper way of
> > validating a virtual interrupt number.
> > 
> > Signed-off-by: Ezequiel Garcia <ezequiel.garcia@free-electrons.com>
> > ---
> >  drivers/net/ethernet/marvell/mvmdio.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/drivers/net/ethernet/marvell/mvmdio.c b/drivers/net/ethernet/marvell/mvmdio.c
> > index b161a52..eb2cabf 100644
> > --- a/drivers/net/ethernet/marvell/mvmdio.c
> > +++ b/drivers/net/ethernet/marvell/mvmdio.c
> > @@ -232,7 +232,7 @@ static int orion_mdio_probe(struct platform_device *pdev)
> >  		clk_prepare_enable(dev->clk);
> >  
> >  	dev->err_interrupt = platform_get_irq(pdev, 0);
> > -	if (dev->err_interrupt != -ENXIO) {
> > +	if (dev->err_interrupt > 0) {
> 
> Ezequiel,
> 
> I cannot find where Rob's mentioned patch set adds -ENODEV, but isn't

Well, I don't think it's not mentioned in the patch. The path is:

platform_get_irq -> of_irq_get -> of_irq_parse_one -> EINVAL.

So it's EINVAL, not ENODEV. But the lesson is to avoid checking for
a particular error (except EPROBE_DEFER which is special) because
it's a fragile practice.

> the semantic for -EPROBE_DEFER: there *should* be an irq, but it is
> not yet available. That basically means, we should also defer on that
> error otherwise we would ignore that we have actually been given an irq
> to work with, right?
> 

Yes, I agree. Did another patch for that, but haven't send it yet.
AFAICS, mvebu platforms will never hit the deferred case as the irqchip
is the first driver registered (as per drivers/Makefile).

Not that we should count on that :)
-- 
Ezequiel García, Free Electrons
Embedded Linux, Kernel and Android Engineering
http://free-electrons.com