Re: [PATCH V6 06/13] arm64, pci, acpi: ACPI support for legacy IRQs parsing and consolidation with DT code.

Lorenzo Pieralisi
2016-04-27T11:46:40Z

On Tue, Apr 26, 2016 at 09:44:30PM -0500, Bjorn Helgaas wrote:
> On Fri, Apr 15, 2016 at 07:06:41PM +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.
>
> Can you be a little more specific about the issue here? I think you
> mean pci_device_add()-time, because that's where we call
> pcibios_add_device. Which ACPI tables are involved? _PRT? Why is
> that a problem? We don't cache those tables any more after
> 181380b702ee ("PCI/ACPI: Don't cache _PRT, and don't associate them
> with bus numbers").

https://lists.linaro.org/pipermail/linaro-acpi/2015-October/005944.html

I think it is a scan handler ordering issue and probably by caching
_PRT this problem would not exist but I have to read the commit above
in details to understand if that's the case.

> x86 and ia64 both call acpi_pci_irq_enable() from
> pcibios_enable_device(). Could you do the same on ARM64?
> pcibios_enable_device() happens later than either pci_device_add() or
> pci_device_probe().

We could in theory. In practice we have to see if that triggers DT
regressions on PCI host controllers that do not call pci_fixup_irqs(),
but rely on the legacy IRQ routing to be done in arm64
pcibios_add_device().

> > 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 c72de66..15109c11 100644
> > --- a/arch/arm64/kernel/pci.c
> > +++ b/arch/arm64/kernel/pci.c
> > @@ -50,11 +50,16 @@ 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
>
> Not your problem, but your patch makes it obvious: it's ugly that we
> set dev->irq to the IRQ returned from of_irq_parse_and_map_pci(), but
> acpi_pci_irq_enable() sets dev->irq internally.
>
> x86 also has the situation of calling either acpi_pci_irq_enable() or
> of_irq_parse_and_map_pci(), and it looks like they can even decide at
> run-time as you can here. If we're solving the same problem, can we
> use a similar mechanism? x86 sets a pcibios_enable_irq function
> pointer.

Yes we could, but that's orthogonal to this patch, it's basically
rewriting this code in a different way and adding flexibility to the
function mapping irqs.

Thanks,
Lorenzo

>
> > return 0;
> > }
> > --
> > 1.9.1
> >
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