linux-kernel - Re: [PATCH v8 3/7] PCI: dwc: ep: Add bus_addr

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Message-ID: <20250116224902.GA614046@bhelgaas>
Date: Thu, 16 Jan 2025 16:49:02 -0600
From: Bjorn Helgaas <helgaas@...nel.org>
To: Frank Li <Frank.li@....com>
Cc: Rob Herring <robh@...nel.org>, Saravana Kannan <saravanak@...gle.com>,
	Jingoo Han <jingoohan1@...il.com>,
	Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>,
	Lorenzo Pieralisi <lpieralisi@...nel.org>,
	Krzysztof Wilczyński <kw@...ux.com>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	Richard Zhu <hongxing.zhu@....com>,
	Lucas Stach <l.stach@...gutronix.de>,
	Shawn Guo <shawnguo@...nel.org>,
	Sascha Hauer <s.hauer@...gutronix.de>,
	Pengutronix Kernel Team <kernel@...gutronix.de>,
	Fabio Estevam <festevam@...il.com>, devicetree@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, imx@...ts.linux.dev
Subject: Re: [PATCH v8 3/7] PCI: dwc: ep: Add bus_addr_base for outbound
 window

On Thu, Jan 16, 2025 at 03:02:44PM -0500, Frank Li wrote:
> On Thu, Jan 16, 2025 at 01:45:58PM -0600, Bjorn Helgaas wrote:
> > 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@...10000  │
> > > > >   │                             ┌────────────────┐│
> > > > >   │                             │   Endpoint     ││
> > > > >   │                             │   PCIe         ││
> > > > >   │                             │   Controller   ││
> > > > >   │           bus@...00000      │                ││
> > > > >   │           ┌──────────┐      │                ││
> > > > >   │           │          │ 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@...00000 {
> > > > > 	compatible = "simple-bus";
> > > > > 	ranges = <0x80000000 0x0 0x70000000 0x10000000>;
> > > > >
> > > > > 	pcie-ep@...10000 {
> > > > > 		reg = <0x80000000 0x10000000>;
> > > > > 		reg-names ="addr_space";
> > > > > 		...
> > > > > 	};
> > > > > 	...
> > > > > };
> > > > >
> > > > > 'ranges' in bus@...00000 descript how address map from CPU address to bus
> > > > > address.
> > > >
> > > > Shouldn't there also be a pcie-ep@...10000 '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@...10000 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.
> 
> How about add comments after
> 
> reg-names ="addr_space"; // Indicate EP outbound windows space instead use
> ranges by histortical reason.

OK, that seems reasonable.

Where does the 0xA000_0000 PCI address come from?  I assume that's in
DT somewhere too?

Is there a binding in the tree that would take advantage of this patch
that I can look at?  arch/arm64/boot/dts/freescale/imx8-ss-hsio.dtsi 
has bus@...00000 that does this translation, but I don't see any
endpoint mode that uses it.

> > > 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.
> 
> Okay for name parent_bus_addr.
> Do you need me to respin it? Or you change it by yourself?

I can do that.

Bjorn

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