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

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Date:	Tue, 26 Apr 2016 21:44:30 -0500
From:	Bjorn Helgaas <helgaas@...nel.org>
To:	Tomasz Nowicki <tn@...ihalf.com>
Cc:	arnd@...db.de, will.deacon@....com, catalin.marinas@....com,
	rafael@...nel.org, hanjun.guo@...aro.org,
	Lorenzo.Pieralisi@....com, okaya@...eaurora.org,
	jiang.liu@...ux.intel.com, jchandra@...adcom.com,
	robert.richter@...iumnetworks.com, mw@...ihalf.com,
	Liviu.Dudau@....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
Subject: Re: [PATCH V6 06/13] arm64, pci, acpi: ACPI support for legacy IRQs
 parsing and consolidation with DT code.

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").

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().

> 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 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.

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