linux-kernel - Re: [PATCH v1 1/2] ata: libahci_platform: Get rid of dup message when IRQ can't be retrieved

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Date:   Mon, 13 Dec 2021 13:52:19 +0200
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     Damien Le Moal <damien.lemoal@...nsource.wdc.com>
Cc:     Sergey Shtylyov <s.shtylyov@....ru>, linux-ide@...r.kernel.org,
        linux-kernel@...r.kernel.org, Hans de Goede <hdegoede@...hat.com>,
        Jens Axboe <axboe@...nel.dk>
Subject: Re: [PATCH v1 1/2] ata: libahci_platform: Get rid of dup message
 when IRQ can't be retrieved

On Mon, Dec 13, 2021 at 07:39:31AM +0900, Damien Le Moal wrote:
> On 2021/12/11 19:25, Sergey Shtylyov wrote:
> > On 11.12.2021 2:45, Damien Le Moal wrote:

...

> >>>> So 0 will be returned as-is. That is rather weird. That should be fixed to
> >>>> return -ENXIO:
> >>>>
> >>>> 	if (WARN(ret == 0, "0 is an invalid IRQ number\n"))
> >>>> 		return -ENXIO;
> >>>> 	return ret;
> >>>
> >>>     My unmerged patch (https://marc.info/?l=linux-kernel&m=163623041902285) does this
> >>> but returns -EINVAL instead.
> >>
> >> Thinking more about this, shouldn't this change go into platform_get_irq()
> >> instead of platform_get_irq_optional() ?
> > 
> >     Why? platform_get_irq() currently just calls platform_get_irq_optional()...
> > 
> >> The way I see it, I think that the intended behavior for
> >> platform_get_irq_optional() is:
> >> 1) If have IRQ, return it, always > 0
> >> 2) If no IRQ, return 0
> > 
> >     That does include the IRQ0 case, right?
> 
> IRQ 0 being invalid, I think that case should be dealt with internally within
> platform_get_irq_optional() and warn/error return. IRQ 0 showing up would thus
> be case (3), an error.
> 
> > 
> >> 3) If error, return < 0
> >> no ?
> > 
> >    I completely agree, I (after thinking a bit) have no issues with that...
> > 
> >> And for platform_get_irq(), case (2) becomes an error.
> >> Is this the intended semantic ?
> > 
> >     I don't see how it's different from the current behavior. But we can do 
> > that as well, I just don't see whether it's really better...
> 
> The problem I see is that the current behavior is unclear: what does
> platform_get_irq_optional() returning 0 mean ? IRQ == 0 ? or "no IRQ" ? I think
> it should be the latter rather than the former. Note that the function could
> return ENOENT (or similar) for the "no IRQ" case. With that, case (2) goes away,
> but then I do not see any difference between platform_get_irq_optional() and
> platform_get_irq().
> 
> If the preferred API semantic is to allow returning IRQ 0 with a warning, then
> the kdoc comments of platform_get_irq_optional() and platform_get_irq() are
> totally broken, and the code for many drivers is probably wrong too.

Yeah, what we need to do is that (roughly a roadmap):
 - revisit callers of platform_get_irq_optional() to be prepared for
   new behaviour
 - rewrite platform_get_irq() to return -ENOENT
 - rewrite platform_get_irq_optional() to return 0 on -ENOENT

This is how other similar (i.e. _optional) APIs do.

-- 
With Best Regards,
Andy Shevchenko