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SubjectRe: [PATCH RESEND v1 1/2] ACPI/PCI: Make _SRS optional for link device
On Fri, Jul 1, 2022 at 6:17 PM Pierre Gondois <pierre.gondois@arm.com> wrote:
>
> From: Pierre Gondois <Pierre.Gondois@arm.com>
>
> In ACPI 6.4, s6.2.13 "_PRT (PCI Routing Table)", PCI legacy
> interrupts can be described though a link device (first model).
> From s6.2.16 "_SRS (Set Resource Settings)":
> "This optional control method [...]"
>
> Make it optional to have a _SRS method for link devices.

Note that if _DIS is present, _SRS is necessary to enable the link and
acpi_pci_link_add() evaluates _DIS for all links. So you need to
check both, not just one.

Moreover, it doesn't make much sense to provide _PRS without _SRS and
arguably _PRS is needed if _SRS is present, so this needs to be taken
into account too.

AFAICS, the only valid configuration in which _SRS and _PRS are not
present is when _DIS is not present too, so only _CRS is present and
the IRQ listed by it is actually in use. However, in that case it is
hardly necessary to add a device object for the PCI link device at
all.

> Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=215560
> Signed-off-by: Pierre Gondois <pierre.gondois@arm.com>
> ---
> drivers/acpi/pci_link.c | 7 +++++++
> 1 file changed, 7 insertions(+)
>
> diff --git a/drivers/acpi/pci_link.c b/drivers/acpi/pci_link.c
> index 58647051c948..129e3e7e80ee 100644
> --- a/drivers/acpi/pci_link.c
> +++ b/drivers/acpi/pci_link.c
> @@ -288,6 +288,13 @@ static int acpi_pci_link_set(struct acpi_pci_link *link, int irq)
> if (!irq)
> return -EINVAL;
>
> + if (!acpi_has_method(handle, METHOD_NAME__SRS)) {
> + if (link->irq.active == irq)
> + return 0;
> + acpi_handle_err(handle, "Unable to set IRQ %d: No _SRS.\n", irq);
> + return -ENODEV;
> + }
> +
> resource = kzalloc(sizeof(*resource) + 1, irqs_disabled() ? GFP_ATOMIC: GFP_KERNEL);
> if (!resource)
> return -ENOMEM;
> --
> 2.25.1
>

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