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

Hi Bjorn,

On 21.09.2016 21:18, Bjorn Helgaas wrote:

On Wed, Sep 21, 2016 at 11:58:22AM -0700, Duc Dang wrote:

quoted

On Wed, Sep 21, 2016 at 11:04 AM, Bjorn Helgaas [off-list ref] wrote:

quoted

On Wed, Sep 21, 2016 at 03:05:49PM +0100, Lorenzo Pieralisi wrote:

quoted

quoted

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