Subject: [PATCH V4 2/3] Revert "ACPI,PCI,IRQ: remove SCI penalize function"

From: [email-masked] (Bjorn Helgaas)
Date: Fri, 21 Oct 2016 09:45:35 -0500

On Thu, Oct 20, 2016 at 08:58:14PM -0500, Bjorn Helgaas wrote:
> On Wed, Oct 19, 2016 at 06:21:03PM -0400, Sinan Kaya wrote:
> > The SCI penalize function was removed in two steps (first refactor
> > and then remove) and these changes are reverted here in one go.
> > 
> > The commit 103544d86976 ("ACPI,PCI,IRQ: reduce resource requirements")
> > refactored the original code so that SCI penalty is calculated dynamically
> > by the time get_penalty function is called. That change is partially
> > reverted here, specifically for the SCI IRQ alone.
> > 
> > The SCI penalize function was finally dropped by commit 9e5ed6d1fb87
> > ("ACPI,PCI,IRQ: remove SCI penalize function") that replaced the old SCI
> > penalty API with penalty calculation carried out dynamically and based
> > on the acpi_gbl_FADT.sci_interrupt value.
> > 
> > However, that new algorithm relies on the accurate setting of IRQ
> > types and that doesn't happen early enough on some platforms which
> > leads to incorrect penalty assignments for PCI IRQs.  In those cases,
> > irq_get_trigger_type() returns incorrect values for the IRQs in
> > question, because they have not been registered yet by the time the
> > penalties are calculated.
> > 
> > To fix this problem, we only need to fix the penalty for the SCI interrupt.
> > It seems better to add a single "sci_penalty" variable, set it to
> > PIRQ_PENALTY_PCI_USING if it's level/low or PIRQ_PENALTY_ISA_ALWAYS
> > otherwise, and add "sci_penalty" in when appropriate.  That should fix it
> > for *any* SCI IRQ, not just those less than 256, and we don't have to add
> > these extra penalty table entries that are all unused (except possibly for
> > one entry if we have an SCI in the 16-255 range).
> > 
> > For this reason, revert commit 9e5ed6d1fb87 ("ACPI,PCI,IRQ: remove SCI
> > penalize function") completely to restore the correct behavior.
> 
> I like this patch fine, except for the changelog.  I don't think it's
> useful to describe this as a revert and give all the historical
> details.  I think the important part is something like this:
> 
>   We previously used irq_get_trigger_type(irq) to help compute the
>   penalty for the SCI, but that depends on the SCI having been
>   registered already.  Add acpi_penalize_sci_irq() so platforms can
>   tell us the SCI IRQ, trigger, and polarity so we can compute the
>   penalty even before the SCI has been registered.

Thanks for the pointer [1] to the issues around
acpi_penalize_sci_irq() being called before kmalloc() is available.
That begs the question of exactly *why* we need
acpi_penalize_sci_irq() so early -- I doubt we actually need to handle
SCIs that early, and obviously we don't need to look up penalties that
early (because we only look them up when enabling interrupt links,
which happens much later).

[1] http://marc.info/?l=linux-acpi&m=145580159209240&w=2)

> Acked-by: Bjorn Helgaas <[email-masked]>

Wait a minute, I still have a question here: what about other ACPI
arches (ia64, arm64)?  Don't they need to call acpi_penalize_sci_irq()
somewhere?

> > ---
> >  arch/x86/kernel/acpi/boot.c |  1 +
> >  drivers/acpi/pci_link.c     | 30 +++++++++++++++---------------
> >  include/linux/acpi.h        |  1 +
> >  3 files changed, 17 insertions(+), 15 deletions(-)
> > 
> > diff --git a/arch/x86/kernel/acpi/boot.c b/arch/x86/kernel/acpi/boot.c
> > index 90d84c3..0ffd26e 100644
> > --- a/arch/x86/kernel/acpi/boot.c
> > +++ b/arch/x86/kernel/acpi/boot.c
> > @@ -453,6 +453,7 @@ static void __init acpi_sci_ioapic_setup(u8 bus_irq, u16 polarity, u16 trigger,
> >  		polarity = acpi_sci_flags & ACPI_MADT_POLARITY_MASK;
> >  
> >  	mp_override_legacy_irq(bus_irq, polarity, trigger, gsi);
> > +	acpi_penalize_sci_irq(bus_irq, trigger, polarity);
> >  
> >  	/*
> >  	 * stash over-ride to indicate we've been here
> > diff --git a/drivers/acpi/pci_link.c b/drivers/acpi/pci_link.c
> > index 4f37938..294b190 100644
> > --- a/drivers/acpi/pci_link.c
> > +++ b/drivers/acpi/pci_link.c
> > @@ -87,6 +87,7 @@ struct acpi_pci_link {
> >  
> >  static LIST_HEAD(acpi_link_list);
> >  static DEFINE_MUTEX(acpi_link_lock);
> > +static int sci_irq = -1, sci_penalty;
> >  
> >  /* --------------------------------------------------------------------------
> >                              PCI Link Device Management
> > @@ -496,25 +497,13 @@ static int acpi_irq_get_penalty(int irq)
> >  {
> >  	int penalty = 0;
> >  
> > -	/*
> > -	* Penalize IRQ used by ACPI SCI. If ACPI SCI pin attributes conflict
> > -	* with PCI IRQ attributes, mark ACPI SCI as ISA_ALWAYS so it won't be
> > -	* use for PCI IRQs.
> > -	*/
> > -	if (irq == acpi_gbl_FADT.sci_interrupt) {
> > -		u32 type = irq_get_trigger_type(irq) & IRQ_TYPE_SENSE_MASK;
> > -
> > -		if (type != IRQ_TYPE_LEVEL_LOW)
> > -			penalty += PIRQ_PENALTY_ISA_ALWAYS;
> > -		else
> > -			penalty += PIRQ_PENALTY_PCI_USING;
> > -	}
> > +	if (irq == sci_irq)
> > +		penalty += sci_penalty;
> >  
> >  	if (irq < ACPI_MAX_ISA_IRQS)
> >  		return penalty + acpi_isa_irq_penalty[irq];
> >  
> > -	penalty += acpi_irq_pci_sharing_penalty(irq);
> > -	return penalty;
> > +	return penalty + acpi_irq_pci_sharing_penalty(irq);
> >  }
> >  
> >  int __init acpi_irq_penalty_init(void)
> > @@ -881,6 +870,17 @@ bool acpi_isa_irq_available(int irq)
> >  		    acpi_irq_get_penalty(irq) < PIRQ_PENALTY_ISA_ALWAYS);
> >  }
> >  
> > +void acpi_penalize_sci_irq(int irq, int trigger, int polarity)
> > +{
> > +	sci_irq = irq;
> > +
> > +	if (trigger == ACPI_MADT_TRIGGER_LEVEL &&
> > +	    polarity == ACPI_MADT_POLARITY_ACTIVE_LOW)
> > +		sci_penalty = PIRQ_PENALTY_PCI_USING;
> > +	else
> > +		sci_penalty = PIRQ_PENALTY_ISA_ALWAYS;
> > +}
> > +
> >  /*
> >   * Over-ride default table to reserve additional IRQs for use by ISA
> >   * e.g. acpi_irq_isa=5
> > diff --git a/include/linux/acpi.h b/include/linux/acpi.h
> > index c5eaf2f..67d1d3e 100644
> > --- a/include/linux/acpi.h
> > +++ b/include/linux/acpi.h
> > @@ -318,6 +318,7 @@ struct pci_dev;
> >  int acpi_pci_irq_enable (struct pci_dev *dev);
> >  void acpi_penalize_isa_irq(int irq, int active);
> >  bool acpi_isa_irq_available(int irq);
> > +void acpi_penalize_sci_irq(int irq, int trigger, int polarity);
> >  void acpi_pci_irq_disable (struct pci_dev *dev);
> >  
> >  extern int ec_read(u8 addr, u8 *val);
> > -- 
> > 1.9.1
> > 
> > 
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