Re: [PATCH V1 1/2] PCI: thunder: Enable ACPI PCI controller for ThunderX pass2.x silicon version

[Bjorn Helgaas <helgaas@kernel.org>]

On Wed, Nov 30, 2016 at 08:00:12PM -0500, Sinan Kaya wrote:
> Hi Bjorn,
> 
> On 11/30/2016 7:28 PM, Bjorn Helgaas wrote:
> > Actually, that raises a question for qualcomm and hisi: in the DT
> > model, we use non-ECAM config accessors in the driver, but in the ACPI
> > model, we use ECAM accessors.  It seems like the accessors should be
> > the same regardless of whether we discover the bridge via DT or ACPI.
> 
> For servers, we are only setting up the PCIe controller in ECAM mode in FW.
> If somebody wants to use DT with QCOM Server (unsupported but possible),
> they need to use pci-host-ecam-generic driver.
> 
> Here is an example:
> 
> 	pcie3 {
> 		compatible = "pci-host-ecam-generic";
> 		device_type = "pci";
> 		#address-cells = <3>;
> 		#size-cells = <2>;
> 		bus-range = <0x0 0xff>;
> 		linux,pci-domain = <3>;
> 
> 		// CPU_PHYSICAL(2)  SIZE(2)
> 		reg = <0xC00 0x00000000  0x0 0x10000000>;
>  	...
> 	}
> 
> I think you are referring to this driver here.
> 
> obj-$(CONFIG_PCIE_QCOM) += pcie-qcom.o
> 
> This driver is only in use by the mobile products.

https://git.kernel.org/cgit/linux/kernel/git/helgaas/pci.git/commit/?h=pci/ecam&id=2bb62a60711e
says it's for the Qualcomm QDF2432.  Is pcie-qcom for that same
device, or is it for something different?

I assume it's probably different because pci-host-ecam-generic uses
the standard ECAM accessors (pci_generic_ecam_ops), while the quirk
requires non-standard ones (pci_32b_ops).

If these are two different controllers, that's fine.  If it's the same
controller in both cases, the controller should be configured the same
way (either by FW or by the DT driver) and we should use the same
accessors.

If you have to use different accessors for the same controller, you
would need some explanation for the difference because it's a
maintenance headache to operate a device in different modes depending
on the environment or which driver you're using.

Bjorn