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

[Andy Shevchenko <andriy.shevchenko@linux.intel.com>]

On Fri, Dec 10, 2021 at 02:14:15PM +0300, Sergey Shtylyov wrote:
> On 12/10/21 1:44 PM, Andy Shevchenko wrote:
> 
> >>>>>>> While at it, drop redundant check for 0 as platform_get_irq() spills
> >>>>>>> out a big WARN() in such case.
> >>>>>>
> >>>>>>    And? IRQ0 is still returned! :-(
> >>>>>
> >>>>> It should not be returned in the first place.
> >>>>
> >>>>    But it still is, despite the WARN(), right?
> >>>
> >>> So, you admit that there is a code which does that?
> >>
> >>    I admit *what*?! That platfrom_get_irq() and its ilk return IRQ0 while they
> >> shouldn't? =)
> > 
> > That there is a code beneath platform_get_irq() that returns 0, yes.
> 
>    Look at the ACPI-specific GpioInt handling code (just above the out_not_found label) --
> I'm not sure the check there is correct -- I'm not very familiar with ACPI, you seem to
> know it much better. :-)

And what is your point here exactly? If == 0 case happens, it will be
immediately WARN() and reported (I hope) since it will mean bug in the code.

>    Also, 0 can be specified via the normal IRQ resource. I know of e.g. the Alchemy MIPS SoCs
> that have IRQ0 used by UART0; luckily, currently SoC IRQs are mapped starting at Linux IRQ8
> (but it wasn't the case in the 2.6.1x time frame where we had issue with the serial driver)...

You mixed up HW IRQ with vIRQ. The former one may be 0 and it's completely valid case, while
the second one is not.

> >>> That code should be fixed first. Have you sent a patch?
> >>
> >>    Which code?! You got me totally muddled. =)
> > 
> > Above mentioned.
> 
>    What needs to be fixed in this case is the interrupt controller driver.

What do you mean by that? vIRQ is handled by IRQ core, IRQ controller driver
just a mere provider of the resource. And those exceptions for vIRQ == 0
shouldn't be propagated to the platform code or so.

> Quoting Linus
> (imprecisely :-)), IRQ #s should be either mapped starting with #1 or IRQ0 remapped at
> the end of the controller's interrupt range... I currently have no information on the
> platforms requiring such kind of fixing (Alchemy don't seem to need it now)...

Again, do not mix vIRQ (about which Linus ranted) and HW IRQ.

...

> >>>>>>> -	if (!irq)
> >>>>>>> -		return -EINVAL;
> >>>>>>
> >>>>>>    This is prermature -- let's wait till my patch that stops returning IRQ0 from
> >>>>>> platform_get_irq() and friends gets merged....
> >>>>>
> >>>>> What patch?
> >>>>
> >>>>    https://marc.info/?l=linux-kernel&m=163623041902285
> >>>>
> >>>>> Does it fix platform_get_irq_optional()?
> >>>>
> >>>>    Of course! :-)
> >>>
> >>> Can you share link to lore.kernel.org, please?
> >>> It will make much easier to try and comment.
> >>
> >>    I don't know how to uise it yet, and I'm a little busy with other IRQ0 issues ATM,

>    A little bit, I meant to type.

No problem. I just haven't got what other IRQ0 issues except fixing
platform_get_irq_optional() et al. could be possibly needed...

> >> so I'm afraid you're on your own here...
> > 
> > lore.kernel.org is the official mailing list archive for Linux kernel work
> > AFAIU. Other sites may do whatever they want with that information, so -->
> > they are unreliable. If you wish to follow the better process, use
> > lore.kernel.org. Understanding how it works takes no more than 5 minutes
> > by engineer with your kind of experience with Linux kernel development.
> 
>    OK, I'll explore this archive when I have time. BTW, does it keep the messages not
> posted to LKML (I tend to only CC LKML if there's no other mailing lists to post to)?

TL;DR: yes.

-- 
With Best Regards,
Andy Shevchenko