linux-kernel - Re: [PATCH v8 2/7] PCI: dwc: Use devicetree 'ranges' property to get rid of cpu_addr

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Message-ID: <Z4p6bekWQ7t7ZDS8@lizhi-Precision-Tower-5810>
Date: Fri, 17 Jan 2025 10:42:37 -0500
From: Frank Li <Frank.li@....com>
To: Bjorn Helgaas <helgaas@...nel.org>
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 2/7] PCI: dwc: Use devicetree 'ranges' property to get
 rid of cpu_addr_fixup() callback

On Thu, Jan 16, 2025 at 05:29:16PM -0600, Bjorn Helgaas wrote:
> On Thu, Jan 16, 2025 at 05:14:00PM -0600, Bjorn Helgaas wrote:
> > On Tue, Nov 19, 2024 at 02:44:20PM -0500, Frank Li wrote:
> > > parent_bus_addr in struct of_range can indicate address information just
> > > ahead of PCIe controller. Most system's bus fabric use 1:1 map between
> > > input and output address. but some hardware like i.MX8QXP doesn't use 1:1
> > > map. See below diagram:
> > >
> > >             ┌─────────┐                    ┌────────────┐
> > >  ┌─────┐    │         │ IA: 0x8ff8_0000    │            │
> > >  │ CPU ├───►│   ┌────►├─────────────────┐  │ PCI        │
> > >  └─────┘    │   │     │ IA: 0x8ff0_0000 │  │            │
> > >   CPU Addr  │   │  ┌─►├─────────────┐   │  │ Controller │
> > > 0x7ff8_0000─┼───┘  │  │             │   │  │            │
> > >             │      │  │             │   │  │            │   PCI Addr
> > > 0x7ff0_0000─┼──────┘  │             │   └──► IOSpace   ─┼────────────►
> > >             │         │             │      │            │    0
> > > 0x7000_0000─┼────────►├─────────┐   │      │            │
> > >             └─────────┘         │   └──────► CfgSpace  ─┼────────────►
> > >              BUS Fabric         │          │            │    0
> > >                                 │          │            │
> > >                                 └──────────► MemSpace  ─┼────────────►
> > >                         IA: 0x8000_0000    │            │  0x8000_0000
> > >                                            └────────────┘
> > >
> > > bus@...00000 {
> > > 	compatible = "simple-bus";
> > > 	#address-cells = <1>;
> > > 	#size-cells = <1>;
> > > 	ranges = <0x80000000 0x0 0x70000000 0x10000000>;
> > >
> > > 	pcie@...10000 {
> > > 		compatible = "fsl,imx8q-pcie";
> > > 		reg = <0x5f010000 0x10000>, <0x8ff00000 0x80000>;
> > > 		reg-names = "dbi", "config";
> > > 		#address-cells = <3>;
> > > 		#size-cells = <2>;
> > > 		device_type = "pci";
> > > 		bus-range = <0x00 0xff>;
> > > 		ranges = <0x81000000 0 0x00000000 0x8ff80000 0 0x00010000>,
> > > 			 <0x82000000 0 0x80000000 0x80000000 0 0x0ff00000>;
> > > 	...
> > > 	};
> > > };
> > >
> > > Term internal address (IA) here means the address just before PCIe
> > > controller. After ATU use this IA instead CPU address, cpu_addr_fixup() can
> > > be removed.
> >
> > > @@ -730,9 +779,15 @@ static int dw_pcie_iatu_setup(struct dw_pcie_rp *pp)
> > >
> > >  		atu.index = i;
> > >  		atu.type = PCIE_ATU_TYPE_MEM;
> > > -		atu.cpu_addr = entry->res->start;
> > > +		parent_bus_addr = entry->res->start;
> > >  		atu.pci_addr = entry->res->start - entry->offset;
> > >
> > > +		ret = dw_pcie_get_parent_addr(pci, entry->res->start, &parent_bus_addr);
> > > +		if (ret)
> > > +			return ret;
> > > +
> > > +		atu.cpu_addr = parent_bus_addr;
> >
> > Here you set atu.cpu_addr to the intermediate bus address instead
> > of the CPU physical address before calling
> > dw_pcie_prog_outbound_atu().
> >
> > But what about other callers of dw_pcie_prog_outbound_atu()?  Don't
> > all of them need to use the intermediate bus address?

All should use "intermediate bus address", RC side only call it here. EP

side is here
https://lore.kernel.org/imx/Z4p0fUAK1ONNjLst@lizhi-Precision-Tower-5810/T/#t

>
> Somehow I expected the patch to skip calling ->cpu_addr_fixup() if the
> driver had set 'use_parent_dt_ranges'.  In fact, I think that's a
> requirement.

It's fine to add check to call cpu_addr_fixup() although I think driver
owner should take responsiblity to make cpu_addr_fixup and
use_parent_dt_ranges exclusive.

>
> Since dw_pcie_prog_outbound_atu() is the only dwc caller, maybe the
> parent_bus_addr change should go *there* instead of in the callers?

I am not sure I understand your means.

EP and RC parts need call dw_pcie_prog_outbound_atu(). EP and RC use
difference method to get outbound windows informaiton. So can't move it
into dw_pcie_prog_outbound_atu().

Frank
>
> Bjorn