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

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Date:	Mon, 13 Jun 2016 16:56:46 +0100
From:	Liviu.Dudau@....com
To:	Lorenzo Pieralisi <lorenzo.pieralisi@....com>
Cc:	Bjorn Helgaas <helgaas@...nel.org>,
	Tomasz Nowicki <tn@...ihalf.com>, arnd@...db.de,
	will.deacon@....com, catalin.marinas@....com, rafael@...nel.org,
	hanjun.guo@...aro.org, okaya@...eaurora.org, jchandra@...adcom.com,
	robert.richter@...iumnetworks.com, mw@...ihalf.com,
	ddaney@...iumnetworks.com, wangyijing@...wei.com,
	Suravee.Suthikulpanit@....com, msalter@...hat.com,
	linux-pci@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	linux-acpi@...r.kernel.org, linux-kernel@...r.kernel.org,
	linaro-acpi@...ts.linaro.org, jcm@...hat.com,
	andrea.gallo@...aro.org, dhdang@....com, jeremy.linton@....com,
	liudongdong3@...wei.com, cov@...eaurora.org
Subject: Re: [PATCH V9 09/11] ARM64/PCI: ACPI support for legacy IRQs parsing
 and consolidation with DT code

On Mon, Jun 13, 2016 at 11:40:05AM +0100, Lorenzo Pieralisi wrote:
> 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.

Because at that time (September 2014) there was no pcibios_alloc_irq() (added
June 2015 by commit 890e4847587fcf) and after that nobody bothered to update
the arm64 code to make use of the new API.

Best regards,
Liviu

> 
> > 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@...ihalf.com>
> > > Suggested-by: Lorenzo Pieralisi <lorenzo.pieralisi@....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
> > > 
> > 
> 

-- 
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