linux-kernel - Re: [PATCH 2/2] ACPI / PCI: Account for ARI in

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Date:	Tue, 26 May 2015 16:58:52 -0400
From:	Don Dutile <ddutile@...hat.com>
To:	Alex Williamson <alex.williamson@...hat.com>
CC:	linux-acpi@...r.kernel.org, linux-pci@...r.kernel.org,
	bhelgaas@...gle.com, rjw@...ysocki.net,
	linux-kernel@...r.kernel.org, lenb@...nel.org
Subject: Re: [PATCH 2/2] ACPI / PCI: Account for ARI in _PRT lookups

On 05/26/2015 04:42 PM, Alex Williamson wrote:
> On Tue, 2015-05-26 at 16:06 -0400, Don Dutile wrote:
>> On 05/26/2015 01:54 PM, Alex Williamson wrote:
>>> The PCIe specification, rev 3.0, section 2.2.8.1, contains the
>>> following implementation note:
>>>
>>>       Virtual Wire Mapping for INTx Interrupts From ARI Devices
>>>
>>>       The implied Device Number for an ARI Device is 0. When ARI-aware
>>>       software (including BIOS and operating system) enables ARI
>>>       Forwarding in the Downstream Port immediately above an ARI Device
>>>       in order to access its Extended Functions, software must
>>>       comprehend that the Downstream Port will use Device Number 0 for
>>>       the virtual wire mappings of INTx interrupts coming from all
>>>       Functions of the ARI Device. If non-ARI-aware software attempts
>>>       to determine the virtual wire mappings for Extended Functions, it
>>>       can come up with incorrect mappings by examining the traditional
>>>       Device Number field and finding it to be non-0.
>>>
>>> We account for this in pci_swizzle_interrupt_pin(), but it looks like
>>> we miss it here, looking for a _PRT entry with a slot matching the
>>> ARI device slot number.  This can cause errors like:
>>>
>>> pcieport 0000:80:03.0: can't derive routing for PCI INT B
>>> sfc 0000:82:01.1: PCI INT B: no GSI
>>>
>>> pci_dev.irq is then invalid, resulting in errors for drivers that
>>> attempt to enable INTx on the device.  Fix by using slot 0 for ARI
>>> enabled devices.
>>>
>>> Signed-off-by: Alex Williamson <alex.williamson@...hat.com>
>>> ---
>>>    drivers/acpi/pci_irq.c |    4 ++--
>>>    1 file changed, 2 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/drivers/acpi/pci_irq.c b/drivers/acpi/pci_irq.c
>>> index b1def41..65e83cd 100644
>>> --- a/drivers/acpi/pci_irq.c
>>> +++ b/drivers/acpi/pci_irq.c
>>> @@ -163,7 +163,7 @@ static int acpi_pci_irq_check_entry(acpi_handle handle, struct pci_dev *dev,
>>>    {
>>>    	int segment = pci_domain_nr(dev->bus);
>>>    	int bus = dev->bus->number;
>>> -	int device = PCI_SLOT(dev->devfn);
>>> +	int device = pci_ari_enabled(dev->bus) ? 0 : PCI_SLOT(dev->devfn);
>>>    	struct acpi_prt_entry *entry;
>>>
>>>    	if (((prt->address >> 16) & 0xffff) != device ||
>>> @@ -181,7 +181,7 @@ static int acpi_pci_irq_check_entry(acpi_handle handle, struct pci_dev *dev,
>>>    	 */
>>>    	entry->id.segment = segment;
>>>    	entry->id.bus = bus;
>>> -	entry->id.device = (prt->address >> 16) & 0xFFFF;
>>> +	entry->id.device = PCI_SLOT(dev->devfn);
>> I would expect that this should be = device, not PCI_SLOT(dev->devfn),
>> esp if used by ACPI core, since it'll be expecting a swizzle from device 0,
>> per above spec.
>
> But it's not used by ACPI core.
>
>> Additionally, if you look at the beginning of this function, this check is performed:
>>          if (((prt->address >> 16) & 0xffff) != device ||
>>               prt->pin + 1 != pin)
>>                   return -ENODEV;
>>
>> So, that implies you leave this assignment as is,
>> or set it to device -- six of one, half-dozen another.
>
> TBH, I didn't really know what to do with this field.  struct
> acpi_prt_entry is defined locally to this file, so we're not passing it
> out to ACPI core for anything.  The only consumer of entry.id in this
> call path is the debug print at the bottom of the function:
Well, do_prt_fixups(entry, prt) is called right after the setting,
and although your patch leaves the state of id.device as it was before
to enable the matches in the current list, that may not be so later.

I'd leave the id.device as it was -- set to prt->address >> 16) & 0xFFFF
for the proper matching all around.

if you want the printf to change, patch it to use PCI_SLOT(dev->devfn) instead of entry->id.device.


>
>          ACPI_DEBUG_PRINT_RAW((ACPI_DB_INFO,
>                                "      %04x:%02x:%02x[%c] -> %s[%d]\n",
>                                entry->id.segment, entry->id.bus,
>                                entry->id.device, pin_name(entry->pin),
>                                prt->source, entry->index));
>
> Which is the reason I chose to use the value that I did, because using
> 'device', aka 0, in the ARI path would be confusing.
>
> I think that the only reason entry.id exists is for the fixup code in
> this file.  I'm happy to leave it as 'device' or the original
> '(prt->address >> 16) & 0xFFFF', but what I have feels more correct for
> the debug printk if nothing else.  Thanks,
>
> Alex
>
>>>    	entry->pin = prt->pin + 1;
>>>
>>>    	do_prt_fixups(entry, prt);
>>>
>>> --
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>>>
>>
>
>
>

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