Re: [PATCH V6 3/5] PCI: thunder-pem: Allow to probe PEM-specific register range for ACPI case

[Tomasz Nowicki]

Hi Bjorn,

On 21.09.2016 21:18, Bjorn Helgaas wrote:
> On Wed, Sep 21, 2016 at 11:58:22AM -0700, Duc Dang wrote:
> > On Wed, Sep 21, 2016 at 11:04 AM, Bjorn Helgaas <helgaas@xxxxxxxxxx> wrote:
> > > On Wed, Sep 21, 2016 at 03:05:49PM +0100, Lorenzo Pieralisi wrote:
>
> > > The existing x86 practice is to use PNP0C02 devices for this purpose,
> > > and I think we should just follow that practice.
> > >
> > > ...
> > >
> > > My point is that the hard-coding should not be buried in a driver
> > > where it's invisible to the rest of the kernel.  If we hard-code it in
> > > a quirk that adds _CRS entries, then the kernel will work just like it
> > > would if the firmware had been correct in the first place.  The
> > > resource will appear in /sys/devices/pnp*/*/resources and /proc/iomem,
> > > and if we ever used _SRS to assign or move ACPI devices, we would know
> > > to avoid the bridge resource.
> >
> > Are you suggesting to add code similar to functions in
> > linux/drivers/pnp/quirks.c to declare/attach the additional resource
> > that the host need to have when the resource is not in MCFG table?
>
> Yes, but what I'm suggesting is actually a little stronger.  This has
> nothing to do with whether a resource is in the MCFG table or not.
>
> I'm suggesting ACPI firmware should always describe the resource.  If the
> firmware is defective and doesn't describe it, we should add a quirk in
> pnp/quirks.c to add a resource for it.

Thanks for pointers Bjorn.

ThunderX is the case where we cannot change firmware, also it has no 
PNP0c02 device in tables. So in order to use pnp/quirks.c we would have 
to fabricate PNP0c02 in kernel and then add quirk entry. I am looking 
for the best place to put such emulation code but it seems not trivial.

Thanks,
Tomasz