Subject: Re: [PATCH v2] of/irq: improve error report on irq discovery process failure

From: "Guilherme G. Piccoli" <[email-masked]>
Date: Mon, 5 Dec 2016 17:01:20 -0200

On 12/05/2016 12:28 PM, Rob Herring wrote:
> On Mon, Dec 5, 2016 at 7:59 AM, Guilherme G. Piccoli
> <[email-masked]> wrote:
>> On PowerPC machines some PCI slots might not have level triggered
>> interrupts capability (also know as level signaled interrupts),
>> leading of_irq_parse_pci() to complain by presenting error messages
>> on the kernel log - in this case, the properties "interrupt-map" and
>> "interrupt-map-mask" are not present on device's node in the device
>> tree.
>>
>> This patch introduces a different message for this specific case,
>> and also reduces its level from error to warning. Besides, we warn
>> (once) that possibly some PCI slots on the system have no level
>> triggered interrupts available.
>> We changed some error return codes too on function of_irq_parse_raw()
>> in order other failure's cases can be presented in a more precise way.
>>
>> Before this patch, when an adapter was plugged in a slot without level
>> interrupts capabilitiy on PowerPC, we saw a generic error message
>> like this:
>>
>>     [54.239] pci 002d:70:00.0: of_irq_parse_pci() failed with rc=-22
>>
>> Now, with this applied, we see the following specific message:
>>
>>     [16.154] pci 0014:60:00.1: of_irq_parse_pci: no interrupt-map found,
>>     INTx interrupts not available
>>
>> Finally, we standardize the error path in of_irq_parse_raw() by always
>> taking the fail path instead of returning directly from the loop.
>>
>> Signed-off-by: Guilherme G. Piccoli <[email-masked]>
>> ---
>>
>> v2:
>>   * Changed function return code to always return negative values;
> 
> Are you sure this is safe? This is tricky because of differing values
> of NO_IRQ (0 or -1).

Thanks Rob, but this is purely bad wording from myself. I'm sorry - I
meant to say that I changed only my positive return code (that was
suggested to be removed in the prior revision) to negative return code!

So, I changed only code I added myself in v1 =)

> 
>>   * Improved/simplified warning outputs;
>>   * Changed some return codes and some error paths in of_irq_parse_raw()
>> in order to be more precise/consistent;
> 
> This too could have some side effects on callers.
> 
> Not saying don't do these changes, just need some assurances this has
> been considered.

Thanks for your attention. I performed a quick investigation before
changing this, all the places that use the return values are just
getting "true/false" information from that, meaning they just are
comparing to 0 basically. So change -EINVAL to -ENOENT wouldn't hurt any
user of these return values, it'll only become more informative IMHO.

Now, regarding the only error path that was changed: for some reason,
this was the only place in which we didn't goto fail label in case of
failure - it was added by a legacy commit from Ben, dated from 2006:
006b64de60 ("[POWERPC] Make OF irq map code detect more error cases").
Then it was carried by Grant Likely's commit 7dc2e1134a ("of/irq: merge
irq mapping code"), 6-year old commit.
I wasn't able to imagine a scenario in which changing this would break
something; I believe the change improve consistency, but I'd remove it
if you or somebody else thinks it worth be removed.

Cheers,

Guilherme

> Rob