Re: [PATCH V4 1/3] ACPI, PCI, IRQ: assign ISA IRQ directly during early boot stages

Bjorn Helgaas
2016-10-21T01:39:39Z

On Wed, Oct 19, 2016 at 06:21:02PM -0400, Sinan Kaya wrote:
> The penalty determination of ISA IRQ goes through 4 paths.
> 1. assign PCI_USING during power up via acpi_irq_penalty_init.
> 2. update the penalty with acpi_penalize_isa_irq function based on the
> active parameter.
> 3. kernel command line penalty update via acpi_irq_penalty_update function.
> 4. increment the penalty as USING right after the IRQ is assign to PCI.
>
> acpi_penalize_isa_irq and acpi_irq_penalty_update functions get called
> before the ACPI subsystem is started.
>
> These API need to bypass the acpi_irq_get_penalty function.

I don't mind this patch, but the changelog doesn't tell me what's
broken and why we need this fix. Apparently acpi_irq_get_penalty()
doesn't work before ACPI is initialized, but I don't see *why* it
wouldn't work.

However, I see one bug it *does* fix: we do not store the SCI penalty
in the acpi_isa_irq_penalty[] table because acpi_isa_irq_penalty[]
only holds ISA IRQ penalties, and there's no guarantee that the SCI is
an ISA IRQ. But prior to this patch, we added in the SCI penalty to
the acpi_isa_irq_penalty[] entry when the SCI was an ISA IRQ, which
makes acpi_irq_get_penalty() return the wrong thing. Consider:

Initially acpi_isa_irq_penalty[9] = 0.
Assume sci_interrupt = 9.
Then acpi_irq_get_penalty(9) returns X.
If we call acpi_penalize_isa_irq(9, 1),
it sets acpi_isa_irq_penalty[9] = X,
and now acpi_irq_get_penalty(9) returns X + X.

I'd propose a changelog like this:

We do not want to store the SCI penalty in the acpi_isa_irq_penalty[]
table because acpi_isa_irq_penalty[] only holds ISA IRQ penalties and
there's no guarantee that the SCI is an ISA IRQ. We add in the SCI
penalty as a special case in acpi_irq_get_penalty().

But if we called acpi_penalize_isa_irq() or acpi_irq_penalty_update()
for an SCI that happened to be an ISA IRQ, they stored the SCI
penalty (part of the acpi_irq_get_penalty() return value) in
acpi_isa_irq_penalty[]. Subsequent calls to acpi_irq_get_penalty()
returned a penalty that included *two* SCI penalties.

If this actually fixes a worse problem related to ACPI initialization,
of course you should detail that.

Acked-by: Bjorn Helgaas <bhelgaas@google.com>

> Signed-off-by: Sinan Kaya <okaya@codeaurora.org>
> ---
> drivers/acpi/pci_link.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/acpi/pci_link.c b/drivers/acpi/pci_link.c
> index c983bf7..4f37938 100644
> --- a/drivers/acpi/pci_link.c
> +++ b/drivers/acpi/pci_link.c
> @@ -849,7 +849,7 @@ static int __init acpi_irq_penalty_update(char *str, int used)
> continue;
>
> if (used)
> - new_penalty = acpi_irq_get_penalty(irq) +
> + new_penalty = acpi_isa_irq_penalty[irq] +
> PIRQ_PENALTY_ISA_USED;
> else
> new_penalty = 0;
> @@ -871,7 +871,7 @@ static int __init acpi_irq_penalty_update(char *str, int used)
> void acpi_penalize_isa_irq(int irq, int active)
> {
> if ((irq >= 0) && (irq < ARRAY_SIZE(acpi_isa_irq_penalty)))
> - acpi_isa_irq_penalty[irq] = acpi_irq_get_penalty(irq) +
> + acpi_isa_irq_penalty[irq] = acpi_isa_irq_penalty[irq] +
> (active ? PIRQ_PENALTY_ISA_USED : PIRQ_PENALTY_PCI_USING);
> }
>
> --
> 1.9.1
>
>
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