Re: [PATCH v8 3/7] PCI: dwc: ep: Add bus_addr_base for outbound window

[Bjorn Helgaas <helgaas@kernel.org>]

On Thu, Jan 16, 2025 at 01:04:16PM -0500, Frank Li wrote:
> On Thu, Jan 16, 2025 at 09:32:39AM -0600, Bjorn Helgaas wrote:
> > On Tue, Nov 19, 2024 at 02:44:21PM -0500, Frank Li wrote:
> > >                    Endpoint
> > >   ┌───────────────────────────────────────────────┐
> > >   │                             pcie-ep@5f010000  │
> > >   │                             ┌────────────────┐│
> > >   │                             │   Endpoint     ││
> > >   │                             │   PCIe         ││
> > >   │                             │   Controller   ││
> > >   │           bus@5f000000      │                ││
> > >   │           ┌──────────┐      │                ││
> > >   │           │          │ Outbound Transfer     ││
> > >   │┌─────┐    │  Bus     ┼─────►│ ATU  ──────────┬┬─────►
> > >   ││     │    │  Fabric  │Bus   │                ││PCI Addr
> > >   ││ CPU ├───►│          │Addr  │                ││0xA000_0000
> > >   ││     │CPU │          │0x8000_0000            ││
> > >   │└─────┘Addr└──────────┘      │                ││
> > >   │       0x7000_0000           └────────────────┘│
> > >   └───────────────────────────────────────────────┘
> > >
> > > Use 'ranges' property in DT to configure the iATU outbound window address.
> > > The bus fabric generally passes the same address to the PCIe EP controller,
> > > but some bus fabrics map the address before sending it to the PCIe EP
> > > controller.
> > >
> > > Above diagram, CPU write data to outbound windows address 0x7000_0000, Bus
> > > fabric map it to 0x8000_0000. ATU should use bus address 0x8000_0000 as
> > > input address and map to PCI address 0xA000_0000.
> > >
> > > Previously, 'cpu_addr_fixup()' was used to handle address conversion. Now,
> > > the device tree provides this information, preferring a common method.
> > >
> > > bus@5f000000 {
> > > 	compatible = "simple-bus";
> > > 	ranges = <0x80000000 0x0 0x70000000 0x10000000>;
> > >
> > > 	pcie-ep@5f010000 {
> > > 		reg = <0x80000000 0x10000000>;
> > > 		reg-names ="addr_space";
> > > 		...
> > > 	};
> > > 	...
> > > };
> > >
> > > 'ranges' in bus@5f000000 descript how address map from CPU address to bus
> > > address.
> >
> > Shouldn't there also be a pcie-ep@5f010000 'ranges' property to
> > describe the translation for the window from bus addr 0x8000_0000 to
> > PCI addr 0xA000_0000?
> 
> Needn't 'ranges' under pcie-ep@5f010000 because history reason. DWC use
> reg-names "addr_space" descript outbound windows space.

If reg-name "addr_space" is used instead of 'ranges' for some
historical reason, we should mention that in the commit log so people
don't assume that this difference is the way it's *supposed* to be
done.

I only see "addr_space" mentioned in
Documentation/devicetree/bindings/pci/*-ep.yaml, so I assume
this "addr_space" usage only applies to endpoints?  

> > > Use `of_property_read_reg()` to obtain the bus address and set it to the
> > > ATU correctly, eliminating the need for vendor-specific cpu_addr_fixup().
> >
> > Why is this different from [1], where parent_bus_addr comes from the
> > 'ranges' property?  Isn't this the same exact kind of address
> > translation for both RC and EP mode?
> 
> The method is the same, but space means is difference.
> 
> RC side:
>    regs, 1: controller register, 2: config space, (although it should be
> in ranges)
>    ranges, (IO range and Memory range).
> 
> EP side:
>    regs, 1: controller register, 2: outbound windows space.("addr_space")
> 
> All regs need call of_property_read_reg() to get untranslated address.
> ranges:  use "parent_bus_addr" in [1].

I think we should at least use the same name ("parent_bus_addr", not
"bus_addr_base") and probably also figure out a wrapper or similar way
to use 'ranges' for future endpoint drivers and fall back to
"addr_space" for DWC.

> > [1] https://lore.kernel.org/r/20241119-pci_fixup_addr-v8-1-c4bfa5193288@nxp.com

> > > +++ b/drivers/pci/controller/dwc/pcie-designware.h
> > > @@ -410,6 +410,7 @@ struct dw_pcie_ep {
> > >  	struct list_head	func_list;
> > >  	const struct dw_pcie_ep_ops *ops;
> > >  	phys_addr_t		phys_base;
> > > +	u64			bus_addr_base;
> > >  	size_t			addr_size;
> > >  	size_t			page_size;
> > >  	u8			bar_to_atu[PCI_STD_NUM_BARS];