Re: [PATCH 2/2] ACPI / PCI: Account for ARI in _PRT lookups

[Alex Williamson <alex.williamson@redhat.com>]

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@redhat.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:

        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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