Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
        id S1755286AbdDRMyi (ORCPT <rfc822;w@1wt.eu>);
        Tue, 18 Apr 2017 08:54:38 -0400
Received: from Galois.linutronix.de ([146.0.238.70]:51445 "EHLO
        Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
        with ESMTP id S1751467AbdDRMyh (ORCPT
        <rfc822;linux-kernel@vger.kernel.org>);
        Tue, 18 Apr 2017 08:54:37 -0400
Date: Tue, 18 Apr 2017 14:54:32 +0200 (CEST)
From: Thomas Gleixner <tglx@linutronix.de>
To: David Howells <dhowells@redhat.com>
cc: LKML <linux-kernel@vger.kernel.org>, gnomes@lxorguk.ukuu.org.uk,
        gregkh@linuxfoundation.org, Daniel Lezcano <daniel.lezcano@linaro.org>,
        linux-security-module@vger.kernel.org, keyrings@vger.kernel.org,
        Jens Rottmann <JRottmann@LiPPERTEmbedded.de>,
        Andres Salomon <dilinger@queued.net>
Subject: Re: [PATCH 06/38] Annotate hardware config module parameters in
 drivers/clocksource/
In-Reply-To: <10505.1492519386@warthog.procyon.org.uk>
Message-ID: <alpine.DEB.2.20.1704181451500.1659@nanos>
References: <alpine.DEB.2.20.1704151153280.2327@nanos> <alpine.DEB.2.20.1704150746530.2327@nanos> <alpine.DEB.2.20.1704142021320.2327@nanos> <149141141298.29162.5612793122429261720.stgit@warthog.procyon.org.uk> <149141145858.29162.13072730133817038218.stgit@warthog.procyon.org.uk>
 <12228.1492210765@warthog.procyon.org.uk> <15283.1492235470@warthog.procyon.org.uk> <10505.1492519386@warthog.procyon.org.uk>
User-Agent: Alpine 2.20 (DEB 67 2015-01-07)
MIME-Version: 1.0
Content-Type: text/plain; charset=US-ASCII
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org
Content-Length: 1002
Lines: 36

On Tue, 18 Apr 2017, David Howells wrote:
> Thomas Gleixner <tglx@linutronix.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