Subject: Re: [PATCH v1 1/2] ata: libahci_platform: Get rid of dup message when
 IRQ can't be retrieved
To:     Andy Shevchenko <andriy.shevchenko@linux.intel.com>
CC:     <linux-ide@vger.kernel.org>, <linux-kernel@vger.kernel.org>,
        Hans de Goede <hdegoede@redhat.com>,
        Jens Axboe <axboe@kernel.dk>,
        Damien Le Moal <damien.lemoal@opensource.wdc.com>
References: <20211209145937.77719-1-andriy.shevchenko@linux.intel.com>
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From:   Sergey Shtylyov <s.shtylyov@omp.ru>
Organization: Open Mobile Platform
Message-ID: <51c0aa6e-e75f-faa7-b9b1-850684da58c8@omp.ru>
Date:   Fri, 10 Dec 2021 20:39:38 +0300
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On 12/10/21 2:28 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?

   You're saying IRQ0 shouldn't be returned (by the ACPI code) -- from this fragment
we can see that it may be returned...

> If == 0 case happens, it will be
> immediately WARN() and reported (I hope)

   Well, "hope dies last"... :-)

> 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.

   I didn't. Linux expects the vIRQs (I called them Linux IRQs). In the 2.6.1x time frame
those corresponded 1:1 on Alchemy. Also, there's 8259 which is always mapped at vIRQ0 (or
the legacy drivers won't work).

> The former one may be 0 and it's completely valid case, while
> the second one is not.

   Well, request_irq() happilly takes vIRQ0. Moreover, there are 8253 drivers in e.g. the arch/x86/
(PPC and MIPS too) which do use vIRQ0.

>>>>> 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?

   You better ask Linus... ;-)

> 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)...

   Well, actually that Linus' quote predates drivers/irqchip/, so I must confess this
argument was wrong... :-)

> 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...

   There is other IRQ0 issue which is very old already...

[...]

MBR, Sergey