linux-kernel - Re: [PATCH] usb: Replace NO

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Date:   Thu, 6 Oct 2022 09:50:27 -0400
From:   Alan Stern <stern@...land.harvard.edu>
To:     Christophe Leroy <christophe.leroy@...roup.eu>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-kernel@...r.kernel.org, linux-usb@...r.kernel.org
Subject: Re: [PATCH] usb: Replace NO_IRQ by 0

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?

> So use 0 instead of using NO_IRQ.
> 
> Signed-off-by: Christophe Leroy <christophe.leroy@...roup.eu>
> ---
>  drivers/usb/host/ehci-grlib.c  | 2 +-
>  drivers/usb/host/ehci-ppc-of.c | 2 +-
>  drivers/usb/host/fhci-hcd.c    | 2 +-
>  drivers/usb/host/ohci-ppc-of.c | 2 +-
>  drivers/usb/host/uhci-grlib.c  | 2 +-
>  5 files changed, 5 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/usb/host/ehci-grlib.c b/drivers/usb/host/ehci-grlib.c
> index a2c3b4ec8a8b..0717f2ccf49d 100644
> --- a/drivers/usb/host/ehci-grlib.c
> +++ b/drivers/usb/host/ehci-grlib.c
> @@ -99,7 +99,7 @@ static int ehci_hcd_grlib_probe(struct platform_device *op)
>  	hcd->rsrc_len = resource_size(&res);
>  
>  	irq = irq_of_parse_and_map(dn, 0);
> -	if (irq == NO_IRQ) {
> +	if (!irq) {
>  		dev_err(&op->dev, "%s: irq_of_parse_and_map failed\n",
>  			__FILE__);
>  		rv = -EBUSY;

Since NO_IRQ is sometimes set to -1, shouldn't this test (and all the 
other ones you changed) really be doing:

	if (!irq || irq == NO_IRQ) { ...

?

Alan Stern