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

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Message-ID: <20140430114209.GA1907@arch.cereza>
Date:	Wed, 30 Apr 2014 08:42:09 -0300
From:	Ezequiel Garcia <ezequiel.garcia@...e-electrons.com>
To:	Sebastian Hesselbarth <sebastian.hesselbarth@...il.com>
Cc:	netdev@...r.kernel.org,
	Thomas Petazzoni <thomas.petazzoni@...e-electrons.com>,
	Lior Amsalem <alior@...vell.com>,
	Tawfik Bayouk <tawfik@...vell.com>,
	Gregory Clement <gregory.clement@...e-electrons.com>,
	"David S. Miller" <davem@...emloft.net>,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH for v3.15] net: mvmdio: Check for a valid interrupt
 instead of an error

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@...nel.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@...e-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
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