linux-kernel - Re: [PATCH v9 4/7] PCI: dwc: Use devicetree 'ranges' property to get rid of cpu_addr

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Message-ID: <20250226233339.GA562682@bhelgaas>
Date: Wed, 26 Feb 2025 17:33:39 -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,
	Niklas Cassel <cassel@...nel.org>
Subject: Re: [PATCH v9 4/7] PCI: dwc: Use devicetree 'ranges' property to get
 rid of cpu_addr_fixup() callback

On Tue, Jan 28, 2025 at 05:07:37PM -0500, Frank Li wrote:
> parent_bus_offset in resource_entry 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:
> ...

> @@ -448,6 +451,26 @@ int dw_pcie_host_init(struct dw_pcie_rp *pp)
>  	if (IS_ERR(pp->va_cfg0_base))
>  		return PTR_ERR(pp->va_cfg0_base);
>  
> +	if (pci->use_parent_dt_ranges) {
> +		if (pci->ops->cpu_addr_fixup) {
> +			dev_err(dev, "Use parent bus DT ranges, cpu_addr_fixup() must be removed\n");
> +			return -EINVAL;
> +		}
> +
> +		index = of_property_match_string(np, "reg-names", "config");
> +		if (index < 0)
> +			return -EINVAL;
> +
> +		 /*
> +		  * Retrieve the parent bus address of PCI config space.
> +		  * If the parent bus ranges in the device tree provide
> +		  * the correct address conversion information, set
> +		  * 'use_parent_dt_ranges' to true, The
> +		  * 'cpu_addr_fixup()' can be eliminated.
> +		  */
> +		of_property_read_reg(np, index, &pp->cfg0_base, NULL);
> +	}

I think all this code dealing with the "config" resource could go in a
helper function.  It's kind of a lot of clutter in
dw_pcie_host_init().

It would be nice to assign pp->cfg0_base once, not assign res->start
to it and then possibly overwrite it later.

> @@ -841,6 +841,15 @@ void dw_pcie_iatu_detect(struct dw_pcie *pci)
>  	pci->region_align = 1 << fls(min);
>  	pci->region_limit = (max << 32) | (SZ_4G - 1);
>  
> +	if (pci->ops && pci->ops->cpu_addr_fixup) {
> +		/*
> +		 * If the parent 'ranges' property in DT correctly describes
> +		 * the address translation, cpu_addr_fixup() callback is not
> +		 * needed.
> +		 */
> +		dev_warn_once(pci->dev, "cpu_addr_fixup() usage detected. Please fix DT!\n");
> +	}

Can you split the warnings out to a separate patch?  I think we should
warn once in every initialization path where .cpu_addr_fixup() could
be used, i.e.,

  dw_pcie_host_init()
  dw_pcie_ep_init()
  cdns_pcie_host_setup()
  cdns_pcie_ep_setup()

IMO these should warn if .cpu_addr_fixup() is implemented, regardless
of use_parent_dt_ranges.

I'm still puzzling over some of the rest of this, so no need to post a
revised series yet.

Bjorn