Subject: Re: [PATCH/RESEND] arm64: acpi/pci: invoke _DSM whether to preserve firmware PCI setup

From: Bjorn Helgaas <[email-masked]>
Date: Wed, 12 Jun 2019 08:27:30 -0500

On Wed, Jun 12, 2019 at 10:06:06AM +1000, Benjamin Herrenschmidt wrote:
> On Tue, 2019-06-11 at 18:39 -0500, Bjorn Helgaas wrote:

> > This is fine, but can we make a tiny step toward doing this in generic
> > code instead of adding more arch-specific stuff?
> > 
> > E.g., evaluate the _DSM in the generic acpi_pci_root_add(), set a
> > "preserve_config" bit in the struct acpi_pci_root, and test the bit
> > here?
> 
> I'd rather have the flag in the host bridge no ?

Oh, of course, that would make more sense.

> Talking of which, look at the ongoing discussion I have with Lorenzo
> when it comes to pci_bus_claim_resources vs. what x86 does, I'd love
> for you to chime in. I'd like to try to consolidate things further
> accross architectures but there might be reasons I don't see as to why
> things are different in that area, so ...

I don't know any reasons why things are different per arch.  In most
cases I suspect FUD.

Speaking of which, *this* patch looks like FUD because it essentially
says "Linux shouldn't change the PCI configuration on this system" but
it offers no explanation of *why* the config needs to be preserved.  I
would really like some note like "run-time firmware depends on the
addresses of device X".

Bjorn

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