linux-kernel - Re: [PATCH 06/38] Annotate hardware config module parameters in drivers/clocksource/

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Date:   Tue, 18 Apr 2017 14:54:32 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     David Howells <dhowells@...hat.com>
cc:     LKML <linux-kernel@...r.kernel.org>, gnomes@...rguk.ukuu.org.uk,
        gregkh@...uxfoundation.org,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        linux-security-module@...r.kernel.org, keyrings@...r.kernel.org,
        Jens Rottmann <JRottmann@...PERTEmbedded.de>,
        Andres Salomon <dilinger@...ued.net>
Subject: Re: [PATCH 06/38] Annotate hardware config module parameters in
 drivers/clocksource/

On Tue, 18 Apr 2017, David Howells wrote:
> Thomas Gleixner <tglx@...utronix.de> wrote:
> 
> > > > > Btw, is it possible to use IRQ grants to prevent a device that has limited
> > > > > IRQ options from being drivable?
> > > > 
> > > > What do you mean with 'IRQ grants' ?
> > > 
> > > request_irq().
> > 
> > I still can't parse the sentence above. If request_irq() fails the device
> > initialization fails. If you request the wrong irq then request_irq() might
> > succeed but the device won't work.
> 
> I was talking about having using a driver to make request_irq() grant an irq
> to that driver so that another driver can't bind to its device because all its
> irq options are taken and the irqs can't be shared.

Yes. That's possible.

init_driver1()
	request_irq(X, flags,.....);

init_driver2()
	request_irq(X, flags,.....);

The second driver can fail, when flags are not matching. That might be
disagreement about SHARED or the trigger type, i.e. egde vs. level.

Thanks,

	tglx