On Thu, Oct 20, 2016 at 08:39:30PM -0500, Bjorn Helgaas wrote: > 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. Oops, I forgot the penalty we *intended* to add with acpi_penalize_isa_irq(). It's really like this, where X is the SCI penalty and Y is the part added by acpi_penalize_isa_irq(): 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 + Y, and now acpi_irq_get_penalty(9) returns X + X + Y. At the end, acpi_irq_get_penalty(9) *should* return X + Y, but instead it returns X + X + Y, i.e., the SCI penalty is included twice. -- To unsubscribe from this list: send the line "unsubscribe linux-pci" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
