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Date:   Thu, 6 Oct 2022 10:24:42 -0400
From:   Alan Stern <stern@rowland.harvard.edu>
To:     Christophe Leroy <christophe.leroy@csgroup.eu>
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "linux-usb@vger.kernel.org" <linux-usb@vger.kernel.org>
Subject: Re: [PATCH] usb: Replace NO_IRQ by 0
Message-ID: <Yz7lKhs5qUXaoFsF@rowland.harvard.edu>
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On Thu, Oct 06, 2022 at 02:01:57PM +0000, Christophe Leroy wrote:
> 
> 
> Le 06/10/2022 ? 15:50, Alan Stern a ?crit?:
> > On Thu, Oct 06, 2022 at 07:15:44AM +0200, Christophe Leroy wrote:
> >> NO_IRQ is used to check the return of irq_of_parse_and_map().
> >>
> >> On some architecture NO_IRQ is 0, on other architectures it is -1.
> >>
> >> irq_of_parse_and_map() returns 0 on error, independent of NO_IRQ.
> > 
> > This isn't clear.  Does absence of an irq count as an error?  In other
> > words, will irq_of_parse_and_map() sometimes return 0 and other times
> > return NO_IRQ?  What about architectures on which 0 is a valid irq
> > number?
> 
> NO_IRQ doesn't exist anywhere in core functions. Only some drivers and 
> some architectures have relics of it.
> 
> irq_of_parse_and_map() will always return 0 on error.
> 
> 0 can't be a valid logical IRQ number. It may only be a valid hwirq 
> number but it will always be translated to a non-zero logical irq number.
> 
> I'm trying to get rid of NO_IRQ completely in powerpc code, therefore 
> trying to clean-up all drivers used by powerpc architecture.
> 
> Long time ago Linus advocated for not using NO_IRQ, see 
> https://lkml.org/lkml/2005/11/21/221

Okay, good.  Please resubmit the patch and include some of these things 
in the patch description.

Alan Stern