[PATCH V2 1/4] ACPI,PCI,IRQ: factor in PCI possible

[Rafael J. Wysocki]

On Wed, Jun 29, 2016 at 11:21 PM, Sinan Kaya <okaya at codeaurora.org> wrote:
> On 6/29/2016 5:19 PM, Rafael J. Wysocki wrote:
>> On Wed, Jun 29, 2016 at 8:47 PM, Sinan Kaya <okaya at codeaurora.org> wrote:
>>> On 6/29/2016 9:13 AM, Rafael J. Wysocki wrote:
>>>> On Wed, Jun 29, 2016 at 10:27 AM, Sinan Kaya <okaya at codeaurora.org> wrote:
>>>>> The change introduced in commit 103544d86976 ("ACPI,PCI,IRQ: reduce
>>>>> resource requirements") omitted the initially assigned POSSIBLE penalty
>>>>> when the IRQ is active.
>>>>
>>>> It would be good to say what can go wrong with that here.
>>>>
>>>
>>> I can add more description. Here is a first attempt.
>>>
>>> Incorrect calculation of penalty leads to ACPI code assigning the wrong
>>> interrupt number to PCI INTx interrupts.
>>>
>>> This would not be as bad as it sounds in theory. You would just cause the
>>> interrupts to be shared and observe performance penalty.
>>>
>>> However, some drivers like parallel port driver doesn't like interrupt
>>> sharing as in this example and causes all other PCI drivers sharing the interrupt
>>> to malfunction.
>>>
>>> The issue has not been caught because the behavior is platform specific
>>> and depends on the peripheral drivers sharing the IRQ.
>>>
>>> I can claim that this could be a BIOS bug. if interrupt 7 is not good for PCI,
>>> it shouldn't have been listed in the possible PCI interrupts to begin with.
>>> Given this is an existing platform, I don't think we have the luxury to request
>>> all BIOS to be updated. This bugfix is needed to support existing platforms.
>>>
>>>
>>> Feel free to request more information if the above description is not clear.
>>
>> It is clear enough.  I can add it to the changelog when applying the patch.
>
> OK
>
>>
>>>
>>>>> The original code would assign the POSSIBLE value divided by the number
>>>>> of possible IRQs during initialization.
>>>>>
>>>>> Later, if the IRQ is chosen as the active IRQ or if the IRQ is in use
>>>>> by ISA; additional penalties get added.
>>
>> Does "later" here mean "later in that code path" or "in a later patch"?
>
> "later in that code path"

OK

I'm hoping we'll hear from the reporter shortly.

Thanks,
Rafael