Re: [PATCH V6 08/13] PCI: generic, thunder: update to use generic ECAM API

Arnd Bergmann
2016-04-21T09:38:19Z

On Thursday 21 April 2016 11:28:15 Tomasz Nowicki wrote:
> On 19.04.2016 15:06, Arnd Bergmann wrote:
> > On Monday 18 April 2016 21:31:54 Tomasz Nowicki wrote:
> >>
> >> Basically the whole content of pci-thunder-ecam.c and pci-thunder-pem.c.
> >>
> >> pci-thunder-ecam.c contains config space accessors. Similar for
> >> pci-thunder-pem.c but it also has extra init call (it is now called
> >> thunder_pem_init) which finds and maps related registers.
> >
> > They seem to do much more than just override the accessors, they actually
> > change the contents of the config space as well. Is that really necessary
> > on ACPI based systems as well?
>
> Yes, the pci-thunder-ecam.c accessors are meant to emulate config space
> capabilities. They are necessary to synthesize EA capabilities (fixed
> PCI BARs), it wont work without this, for ACPI boot as well.

Why is that? I thought the BARs never get reassigned when using ACPI,
so I'm surprised it's actually needed. Maybe I misunderstood what
you mean by fixed PCI BARs.

> > Another idea: how about moving all of this logic into ACPI and calling
> > some AML method to access the config space if the devices are that
> > far out of spec.
>
> Do you mean Linux specific way to call non-standard config space
> accessors? Then non-standard accessors are going to AML methods which
> are called from common code which handles quirks via unified API ?

What I really meant was a standardized way to do handle hardware that
is in some way or another not compliant with PNP0A08: We could have
a different hardware ID for this and let all the first-generation
ARM servers and also anything else using ACPI with nonstandard PCI
use the same method across operating systems.

Arnd