Re: [RFC] ARM64, PCIe, annd ACPI

[Ray Jui <ray.jui@broadcom.com>]

On 8/7/2018 7:10 PM, Bjorn Helgaas wrote:
> On Tue, Aug 07, 2018 at 05:10:15PM -0700, Ray Jui wrote:
>> Hi Lorenzo/Bjorn,
>>
>> I have a question on PCIe controller APCI support on ARM64 based systems.
>>
>> If my understanding of the implementation of "pci_acpi_scan_root" under
>> "arch/arm64/kernel/pci.c" is correct, it appears
>> "pci_acpi_setup_ecam_mapping" is called within "pci_acpi_scan_root".
>>
>> Does that mean for a PCIe host controller on ARM64 to support ACPI, it needs
>> to support ECAM and MMIO based access to the configuration space registers?
>   
> Yes.  In my opinion, a PCIe host controller is generally required to
> support ECAM even if the platform doesn't support ACPI.  I base this
> on PCIe r4.0, sec 7.2.2:
> 
>    For systems that are PC-compatible, or that do not implement a
>    processor-architecture-specific firmware interface standard that
>    allows access to the Configuration Space, the ECAM is required as
>    defined in this section.
> 
>> If the above statement is true, does it imply that any PCIe controller on
>> ARM64 that does not support MMIO based access to the config space register
>> cannot have ACPI support?
> 
> We would treat that as a non-compliant platform that requires special
> quirks to work around the problem.  That does mean we have to add
> platform-specific quirks, which of course means we can't run an old
> kernel on a new platform that lacks standard ECAM.  There are several
> existing systems like this.
> 
> The notes and examples here should be a place to start:
> 
>    drivers/pci/controller/Makefile
>    drivers/pci/controller/dwc/Makefile
>    drivers/acpi/pci_mcfg.c
> 
> Bjorn
> 

Thanks for the pointers, Bjorn! Very helpful!

Ray