linux-kernel - Re: [PATCH v5 3/3] gpio: grgpio: Add irq support

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Date:	Tue, 23 Apr 2013 13:14:51 +0200
From:	Linus Walleij <linus.walleij@...aro.org>
To:	Andreas Larson <andreas@...sler.com>
Cc:	Grant Likely <grant.likely@...retlab.ca>,
	Rob Herring <rob.herring@...xeda.com>,
	Anton Vorontsov <anton.vorontsov@...aro.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"devicetree-discuss@...ts.ozlabs.org" 
	<devicetree-discuss@...ts.ozlabs.org>, software@...sler.com
Subject: Re: [PATCH v5 3/3] gpio: grgpio: Add irq support

On Mon, Apr 15, 2013 at 2:38 PM, Andreas Larson <andreas@...sler.com> wrote:

> On 2013-04-10 21:25, Linus Walleij wrote:
>>> +int grgpio_irq_map(struct irq_domain *d, unsigned int virq,
(...)
>>> +       /* Request underlying irq if not already requested */
>>> +       lirq->virq = virq;
>>> +       uirq = &priv->uirqs[lirq->index];
>>> +       if (uirq->refcnt == 0) {
>>> +               ret = request_irq(uirq->uirq, grgpio_irq_handler, 0,
>>> +                                 dev_name(priv->dev), priv);
>>
>>
>> No, please request all present uirqs in probe() before creating the
>> irqdomain.
>
>
> The reason for doing it at irq_map and not in probe is that one
> typical hardware setup for this core is that it has irqs that are shared
> with pretty much all other cores in the system. Therefore, if this
> drivers requests all its irqs in the probe function, pretty much all the
> drivers for the other cores in the system that were not lucky enough to
> request their irq before this driver will fail their probes in such a
> hardware setup. This driver can not share irq:s so even if the other
> drivers can handle shared irqs they are out of luck if this driver is
> probed first.
>
> That is why only the irqs that are actually used should be requested and
> thus why the driver does it on demand instead of in the probe.

OK I buy that explanation...

Thanks,
Linus Walleij
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