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

Andy Shevchenko
2021-12-13T11:53:21Z

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