[PATCH] drivers: acpi: fix GIC irq model default PCI IRQ polarity

[Rafael J. Wysocki]

On Mon, Sep 5, 2016 at 4:12 PM, Lorenzo Pieralisi
<lorenzo.pieralisi at arm.com> wrote:
> On ACPI ARM based systems the GIC interrupt controller
> and corresponding interrupt model permit only the high
> polarity for level interrupts.
>
> ACPI firmware describes PCI legacy IRQs through entries
> in the _PRT objects. Entries in the _PRT can be of two types:
>
> - Static: not configurable, trigger/polarity default to level-low,
>   _PRT entry defines the global GSI interrupt number
> - Configurable: _PRT interrupt entry contains a reference to the
>   corresponding PCI interrupt link device (that in turn provides the
>   interrupt descriptor through its _CRS/_PRS methods)
>
> Configurable IRQ entries are not currently allowed by the ACPI
> specification on ARM, since they can only be used for interrupt
> pins that are routable, and ARM platforms GIC configurations
> do not allow dynamic IRQ routing, routing is statically laid out
> at synthesis time; therefore PCI interrupt links cannot be used
> for PCI legacy IRQ descriptions in the _PRT on ARM systems.
>
> On the other hand, current core ACPI code handling PCI legacy IRQs
> consider IRQ trigger/polarity for static _PRT entries as level-low.
>
> On ARM systems with a GIC interrupt controller and corresponding
> ACPI interrupt model this does not work in that GIC interrupt
> controller is only capable of handling level interrupts whose
> polarity is high (for PCI legacy IRQs - that are level-low by
> specification - this means that the legacy IRQs are inverted before
> reaching the interrupt controller pin), resulting in IRQ allocation
> failures such as:
>
> genirq: Setting trigger mode 8 for irq 18 failed (gic_set_type+0x0/0x48)
>
> Change the default polarity for PCI legacy IRQs to high on systems
> booting wth ACPI on platforms with a GIC interrupt controller model,
> fixing the discrepancy between specification and HW behaviour.
>
> Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi at arm.com>
> Cc: Punit Agrawal <punit.agrawal at arm.com>
> Cc: Duc Dang <dhdang at apm.com>
> Cc: Bjorn Helgaas <bhelgaas at google.com>
> Cc: Sinan Kaya <okaya at codeaurora.org>
> Cc: "Rafael J. Wysocki" <rjw at rjwysocki.net>
> Cc: Marc Zyngier <marc.zyngier at arm.com>
> ---
>  drivers/acpi/pci_irq.c | 10 +++++++++-
>  1 file changed, 9 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/acpi/pci_irq.c b/drivers/acpi/pci_irq.c
> index 2c45dd3..c576a6f 100644
> --- a/drivers/acpi/pci_irq.c
> +++ b/drivers/acpi/pci_irq.c
> @@ -411,7 +411,15 @@ int acpi_pci_irq_enable(struct pci_dev *dev)
>         int gsi;
>         u8 pin;
>         int triggering = ACPI_LEVEL_SENSITIVE;
> -       int polarity = ACPI_ACTIVE_LOW;
> +       /*
> +        * On ARM systems with the GIC interrupt model, level interrupts
> +        * are always polarity high by specification; PCI legacy
> +        * IRQs lines are inverted before reaching the interrupt
> +        * controller and must therefore be considered active high
> +        * as default.
> +        */
> +       int polarity = acpi_irq_model == ACPI_IRQ_MODEL_GIC ?
> +                                     ACPI_ACTIVE_HIGH : ACPI_ACTIVE_LOW;
>         char *link = NULL;
>         char link_desc[16];
>         int rc;
> --

Bjorn, any objections?