Re: [RFC] ARM64, PCIe, annd ACPI

From: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
To: Ray Jui <ray.jui@broadcom.com>
Cc: Bjorn Helgaas <bhelgaas@google.com>,
	linux-pci@vger.kernel.org, Tomasz Nowicki <tn@semihalf.com>,
	Vladimir Olovyannikov <vladimir.olovyannikov@broadcom.com>,
	BCM Kernel Feedback <bcm-kernel-feedback-list@broadcom.com>
Subject: Re: [RFC] ARM64, PCIe, annd ACPI
Date: Thu, 9 Aug 2018 09:59:23 +0100	[thread overview]
Message-ID: <20180809085923.GA13428@e107981-ln.cambridge.arm.com> (raw)
In-Reply-To: <a32a8761-f49f-f0cf-928b-0c323c2b540e@broadcom.com>

On Wed, Aug 08, 2018 at 11:49:46AM -0700, Ray Jui wrote:
> 
> 
> On 8/8/2018 2:38 AM, Lorenzo Pieralisi 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?
> >>
> >>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?
> >
> >Yes and it is not just MMIO, config space must be ECAM compliant as described
> >in the PCI firmware specification and enforced here:
> >
> >http://infocenter.arm.com/help/topic/com.arm.doc.den0029b/Server_Base_System_Architecture_v5_0_ARM_DEN_0029B.pdf
> >
> 
> Okay, got it, the SBSA spec makes it very clear that the PCIe controller
> needs to support ECAM.
> 
> >In short: what's in the mainline (+ adequate PCI controller firmware
> >configuration) must be sufficient to bootstrap your PCI subsystem in
> >ACPI, it is a very simple litmus test and we won't add anything that
> >deviates from that to the mainline kernel ARM64 ACPI PCI code support.
> >
> 
> It sounds like I'll have to look into ways to work around this at the driver
> level as Bjorn pointed out with some other examples.

As I said ARM64 ACPI PCI kernel support is in the mainline today and I
am not willing to merge any more MCFG quirks at driver level - the
information is out there, it is public and must be followed, either
designers do that or no ACPI PCI support on your platform, sorry.

Lorenzo