Re: [PATCH v2 2/2] PCI: mediatek-gen3: Configure PBUS_CSR registers for EN7581 SoC

[Bjorn Helgaas <helgaas@kernel.org>]

[+cc Frank, who asked the same question about DT]

On Thu, Feb 20, 2025 at 08:54:06PM +0100, Lorenzo Bianconi wrote:
> On Feb 20, Bjorn Helgaas wrote:
> > On Sun, Feb 02, 2025 at 08:34:24PM +0100, Lorenzo Bianconi wrote:
> > > Configure PBus base address and address mask to allow the hw
> > > to detect if a given address is on PCIE0, PCIE1 or PCIE2.

> > > +#define PCIE_EN7581_PBUS_ADDR(_n)	(0x00 + ((_n) << 3))
> > > +#define PCIE_EN7581_PBUS_ADDR_MASK(_n)	(0x04 + ((_n) << 3))
> > > +#define PCIE_EN7581_PBUS_BASE_ADDR(_n)	\
> > > +	((_n) == 2 ? 0x28000000 :	\
> > > +	 (_n) == 1 ? 0x24000000 : 0x20000000)
> > 
> > Are these addresses something that should be expressed in devicetree?
> 
> Do you have any example/pointer for it?
> 
> > It seems unusual to encode addresses directly in a driver.
> 
> AFAIK they are fixed for EN7581 SoC.

So this is used to detect if a given address is on PCIE0, PCIE1 or
PCIE2.  What does that mean?  There are no other mentions of PCIE0 etc
in the driver, but maybe they match up to "pcie0/1/2" in
arch/arm64/boot/dts/mediatek/mt7988a.dtsi?

It looks like you use PCIE_EN7581_PBUS_ADDR(slot), where "slot" came
from of_get_pci_domain_nr(), which suggests that these might be three
separate Root Ports?

Are we talking about an MMIO address that an endpoint driver uses for
readw() etc, and this code configures the hardware apertures through
the host bridge?  Seems like that would be related to the "ranges"
properties in DT.

Bjorn