Re: [PATCH V9 09/11] ARM64/PCI: ACPI support for legacy IRQs parsing and consolidation with DT code

[Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>]

On Fri, Jun 10, 2016 at 06:36:12PM -0500, Bjorn Helgaas wrote:
> On Fri, Jun 10, 2016 at 09:55:17PM +0200, Tomasz Nowicki wrote:
> > To enable PCI legacy IRQs on platforms booting with ACPI, arch code
> > should include ACPI specific callbacks that parse and set-up the
> > device IRQ number, equivalent to the DT boot path. Owing to the current
> > ACPI core scan handlers implementation, ACPI PCI legacy IRQs bindings
> > cannot be parsed at device add time, since that would trigger ACPI scan
> > handlers ordering issues depending on how the ACPI tables are defined.
> 
> Uh, OK :)  I can't figure out exactly what the problem is here -- I
> don't know where to look if I wanted to fix the scan handler ordering
> issues, and I don't know how I could tell if it would ever be safe to
> move this from driver probe-time back to device add-time.

Right, the commit log could have been more informative.

pcibios_add_device() was added in:

commit d1e6dc91b532 ("arm64: Add architectural support for PCI")

whose commit log does not specify why legacy IRQ parsing should
be done at pcibios_add_device() either, so honestly we had to
do with the information we have at hand.

> I also notice that x86 and ia64 call acpi_pci_irq_enable() even later,
> when the driver *enables* the device.  Is there a reason you didn't do
> it at the same time as x86 and ia64?  This is another of those pcibios
> hooks that really don't do anything arch-specific, so I can imagine
> refactoring this somehow, someday.

Yes, with [1], that was the goal, that stopped because [1] does not
work on x86.

Only DT platform(s) affected by this change are all platforms relying on
drivers/pci/host/pci-xgene.c (others rely on pci_fixup_irqs() that
should be removed too), if on those platforms probing IRQs at device
enable time works ok I can update this patch (it can be done through [1]
once we figure out what to do with it on x86) and move the IRQ set-up at
pcibios_enable_device() time.

@Duc: any feedback on this ?

Thanks,
Lorenzo

[1] http://www.spinics.net/lists/linux-pci/msg45950.html

> Did we have this conversation before?  It seems vaguely familiar, so I
> apologize if you already explained this once.
> 
> > To solve this problem and consolidate FW PCI legacy IRQs parsing in
> > one single pcibios callback (pending final removal), this patch moves
> > DT PCI IRQ parsing to the pcibios_alloc_irq() callback (called by
> > PCI core code at device probe time) and adds ACPI PCI legacy IRQs
> > parsing to the same callback too, so that FW PCI legacy IRQs parsing
> > is confined in one single arch callback that can be easily removed
> > when code parsing PCI legacy IRQs is consolidated and moved to core
> > PCI code.
> > 
> > Signed-off-by: Tomasz Nowicki <tn@semihalf.com>
> > Suggested-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
> > ---
> >  arch/arm64/kernel/pci.c | 11 ++++++++---
> >  1 file changed, 8 insertions(+), 3 deletions(-)
> > 
> > diff --git a/arch/arm64/kernel/pci.c b/arch/arm64/kernel/pci.c
> > index d5d3d26..b3b8a2c 100644
> > --- a/arch/arm64/kernel/pci.c
> > +++ b/arch/arm64/kernel/pci.c
> > @@ -51,11 +51,16 @@ int pcibios_enable_device(struct pci_dev *dev, int mask)
> >  }
> >  
> >  /*
> > - * Try to assign the IRQ number from DT when adding a new device
> > + * Try to assign the IRQ number when probing a new device
> >   */
> > -int pcibios_add_device(struct pci_dev *dev)
> > +int pcibios_alloc_irq(struct pci_dev *dev)
> >  {
> > -	dev->irq = of_irq_parse_and_map_pci(dev, 0, 0);
> > +	if (acpi_disabled)
> > +		dev->irq = of_irq_parse_and_map_pci(dev, 0, 0);
> > +#ifdef CONFIG_ACPI
> > +	else
> > +		return acpi_pci_irq_enable(dev);
> > +#endif
> >  
> >  	return 0;
> >  }
> > -- 
> > 1.9.1
> > 
>