Using the generic host PCIe driver

[Mason]

On 17/02/2017, Bjorn Helgaas wrote:

> I don't know anything about your hardware or environment, but I highly
> encourage you to use [...] generic DT (drivers/pci/host/pci-host-generic.c)
> instead of writing a custom host controller driver.
> 
> The native drivers in drivers/pci/host are a huge maintenance hassle
> for no real benefit.
>
> You're right that the programming model of the host bridge itself is
> not specified by PCI specs, so it's impossible to have a generic
> driver that can manage it completely by itself.
> 
> If you have firmware that initializes the bridge and tells the OS what
> the windows are (bus numbers, memory space, I/O space) and where the
> PCIe-specified ECAM space is, a generic driver can take it from there.

I am currently trying the approach suggested by Bjorn.

This is what my DT node currently looks like:

		pcie at 50000000 {
			compatible = "pci-host-ecam-generic";
			reg = <0x50000000 0x200000>;
			device_type = "pci";
			bus-range = <0>, <1>;
			#size-cells = <2>;
			#address-cells = <3>;
			#interrupt-cells = <1>;
			/* BUS_ADDRESS(3)  CPU_PHYSICAL(1)  SIZE(2) */
			ranges = <0x02000000 0x0 0xa0000000  0xa0000000  0x0 0x00100000>;
		};

(I am aware that interrupt specs are missing, but I hope this
is not a problem at an early stage.)

I.e. the configuration space is at 0x5000_0000
(so bus_0 at 0x5000_0000, and bus_1 at 0x5010_0000)

And I defined a 32-bit non-prefetchable memory space at 0xa0000000

Question 1:
Is there any reason to map CPU address 0xa0000000 anywhere else than
PCI bus address 0xa0000000?


Now, this host controller is revision 1, and as such contains several
"interesting" bugs. How can I work around them in software?


Bug #1

The controller reports an incorrect class. It is a bridge, but it
reports class = 0x048000

AFAICT, tegra had a similar problem, and the solution seems to be
to define a DECLARE_PCI_FIXUP_EARLY hook:

/* Root complex reports incorrect device class */
static void tango_pcie_fixup_class(struct pci_dev *dev)
{
	dev->class = PCI_CLASS_BRIDGE_PCI << 8;
}
DECLARE_PCI_FIXUP_EARLY(0x1105, 0x8758, tango_pcie_fixup_class);

Is that the correct way to work around bug #1


Bug #2

Bus 0 cannot be enumerated, because it reports garbage data for
devices and functions other than 0, i.e. only 0/0/0 works.

How do I work around that issue?


I have a googol more questions, but I'll stick to these for the time being.

Regards.