linux-kernel - Re: [PATCH v2 1/3] of: address: Add cpu_untranslate_addr to struct of_pci

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Message-ID: <20240927235117.GA98484@bhelgaas>
Date: Fri, 27 Sep 2024 18:51:17 -0500
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 v2 1/3] of: address: Add cpu_untranslate_addr to struct
 of_pci_range

On Thu, Sep 26, 2024 at 12:47:13PM -0400, Frank Li wrote:
> Introduce field 'cpu_untranslate_addr' in of_pci_range to retrieve
> untranslated CPU address information. This is required for hardware like
> i.MX8QXP to configure the PCIe controller ATU and eliminate the need for
> workaround address fixups in drivers. Currently, many drivers use
> hardcoded CPU addresses for fixups, but this information is already
> described in the Device Tree. With correct hardware descriptions, such
> fixups can be removed.

Instead of saying "required for hardware like i.MX8QXP", can we say
something specific about what this kind of hardware *does* that
requires this?

I *think* the point is that there's some address translation being
done between the primary and secondary sides of some bridge.

I think "many drivers use hardcoded CPU addresses for fixups"
basically means the .cpu_addr_fixup() callback hardcodes that
translation in the code, e.g., "cpu_addr & CDNS_PLAT_CPU_TO_BUS_ADDR",
"cpu_addr + BUS_IATU_OFFSET", etc, even though those translations
*should* be described via DT.

>             ┌─────────┐                    ┌────────────┐
>  ┌─────┐    │         │ IA: 0x8ff0_0000    │            │
>  │ CPU ├───►│ BUS     ├─────────────────┐  │ PCI        │
>  └─────┘    │         │ IA: 0x8ff8_0000 │  │            │
>   CPU Addr  │ Fabric  ├─────────────┐   │  │ Controller │
> 0x7000_0000 │         │             │   │  │            │
>             │         │             │   │  │            │   PCI Addr
>             │         │             │   └──► CfgSpace  ─┼────────────►
>             │         ├─────────┐   │      │            │    0
>             │         │         │   │      │            │
>             └─────────┘         │   └──────► IOSpace   ─┼────────────►
>                                 │          │            │    0
>                                 │          │            │
>                                 └──────────► MemSpace  ─┼────────────►
>                         IA: 0x8000_0000    │            │  0x8000_0000
>                                            └────────────┘

What does "IA" stand for?

I don't quite understand the mapping done by the "BUS Fabric" block.
It looks like you're saying the CPU Addr 0x7000_0000 is translated to
all three of IA 0x8ff0_0000, IA 0x8ff8_0000, and IA 0x8000_0000, but
that doesn't seem right.

> bus@...00000 {
>         compatible = "simple-bus";
>         #address-cells = <1>;
>         #size-cells = <1>;
>         ranges = <0x5f000000 0x0 0x5f000000 0x21000000>,
>                  <0x80000000 0x0 0x70000000 0x10000000>;
> 
>         pcieb: 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>;
> 	...
> 	};
> };
> 
> 'cpu_untranslate_addr' in of_pci_range can indicate above diagram IA
> address information.
> 
> Signed-off-by: Frank Li <Frank.Li@....com>
> ---
> Change from v1 to v2
> - add cpu_untranslate_addr in of_pci_range, instead adding new API.
> ---
>  drivers/of/address.c       | 2 ++
>  include/linux/of_address.h | 1 +
>  2 files changed, 3 insertions(+)
> 
> diff --git a/drivers/of/address.c b/drivers/of/address.c
> index 286f0c161e332..f4cb82f5313cf 100644
> --- a/drivers/of/address.c
> +++ b/drivers/of/address.c
> @@ -811,6 +811,8 @@ struct of_pci_range *of_pci_range_parser_one(struct of_pci_range_parser *parser,
>  	else
>  		range->cpu_addr = of_translate_address(parser->node,
>  				parser->range + na);
> +
> +	range->cpu_untranslate_addr = of_read_number(parser->range + na, parser->pna);
>  	range->size = of_read_number(parser->range + parser->pna + na, ns);
>  
>  	parser->range += np;
> diff --git a/include/linux/of_address.h b/include/linux/of_address.h
> index 26a19daf0d092..0683ce0c07f68 100644
> --- a/include/linux/of_address.h
> +++ b/include/linux/of_address.h
> @@ -26,6 +26,7 @@ struct of_pci_range {
>  		u64 bus_addr;
>  	};
>  	u64 cpu_addr;
> +	u64 cpu_untranslate_addr;
>  	u64 size;
>  	u32 flags;
>  };
> 
> -- 
> 2.34.1
>