Re: [PATCH v3 2/2] PCI: Add support for Enhanced Allocation devices

[David Daney]

On 09/30/2015 03:50 PM, Sean O. Stalley wrote:
> On Tue, Sep 29, 2015 at 04:53:20PM -0700, David Daney wrote:
> > On 09/29/2015 03:47 PM, Sean O. Stalley wrote:
> > [...]
> > > > > > diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> > > > > > index 6a9a111..7c60b16 100644
> > > > > > --- a/drivers/pci/pci.c
> > > > > > +++ b/drivers/pci/pci.c
> > > > > > @@ -2148,6 +2148,284 @@ void pci_pm_init(struct pci_dev *dev)
> > > > > >   	}
> > > > > >   }
> > > > > >
> > > > > > +static unsigned long pci_ea_set_flags(struct pci_dev *dev, u8 prop)
> > > > > > +{
> > > > > > +	unsigned long flags = IORESOURCE_PCI_FIXED | IORESOURCE_SIZEALIGN;
> > > > >
> > > > > Why did you add the IORESOURCE_SIZEALIGN flag? EA allows for unaligned resources.
> > > >
> > > > pci_bus_assign_resources() fails causing the devices to be unusable
> > > > if resource_alignment() returns zero.  The easiest fix for this was
> > > > to specify IORESOURCE_SIZEALIGN.
> > > >
> > > > An alternative would be to change the code in setup-bus.c so that
> > > > for IORESOURCE_PCI_FIXED resources, it didn't barf.
> > >
> > > I would do this alternative, but with a IORESOURCE_PCI_EA flag.
> >
> > I don't think we need IORESOURCE_PCI_EA.  If a resource is tagged as
> > IORESOURCE_PCI_FIXED that means that it cannot be changed, we
> > shouldn't care why it is fixed (due to an EA capability for
> > example).  We just need to gracefully handle IORESOURCE_PCI_FIXED in
> > the places where things currently go wrong.
> >
> > David Daney
>
> I agree that we need to make sure fixed things stay fixed,
> regardless of if they are fixed by EA or something else.
>
> The question is: do we want to allow all fixed resources to be non-aligned, or just EA?

The alignment should only be important if a new address is being 
calculated for a BAR or behind the bridge memory/io region.  If the 
resource is fixed, I would almost say that "alignment" is an undefined 
concept.  So, in the places were we need special treatment for 
IORESOURCE_PCI_FIXED, I would argue that we shouldn't be use the 
resource alignment information.

David Daney

> -Sean

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