linux-kernel - Re: [PATCH v12 06/13] PCI: dwc: Add dw_pcie_parent_bus

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Message-ID: <20250318153820.GA1001146@bhelgaas>
Date: Tue, 18 Mar 2025 10:38:20 -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>,
	Richard Zhu <hongxing.zhu@....com>,
	Lucas Stach <l.stach@...gutronix.de>,
	Shawn Guo <shawnguo@...nel.org>,
	Sascha Hauer <s.hauer@...gutronix.de>,
	Fabio Estevam <festevam@...il.com>,
	Niklas Cassel <cassel@...nel.org>,
	Pengutronix Kernel Team <kernel@...gutronix.de>,
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-pci@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	imx@...ts.linux.dev, Bjorn Helgaas <bhelgaas@...gle.com>
Subject: Re: [PATCH v12 06/13] PCI: dwc: Add dw_pcie_parent_bus_offset()
 checking and debug

On Sat, Mar 15, 2025 at 03:15:41PM -0500, Bjorn Helgaas wrote:
> From: Frank Li <Frank.Li@....com>
> 
> dw_pcie_parent_bus_offset() looks up the parent bus address of a PCI
> controller 'reg' property in devicetree.  If implemented, .cpu_addr_fixup()
> is a hard-coded way to get the parent bus address corresponding to a CPU
> physical address.
> 
> Add debug code to compare the address from .cpu_addr_fixup() with the
> address from devicetree.  If they match, warn that .cpu_addr_fixup() is
> redundant and should be removed; if they differ, warn that something is
> wrong with the devicetree.
> 
> If .cpu_addr_fixup() is not implemented, the parent bus address should be
> identical to the CPU physical address because we previously ignored the
> parent bus address from devicetree.  If the devicetree has a different
> parent bus address, warn about it being broken.

> +++ b/drivers/pci/controller/dwc/pcie-designware.c
> @@ -1114,7 +1114,8 @@ resource_size_t dw_pcie_parent_bus_offset(struct dw_pcie *pci,
>  	struct device *dev = pci->dev;
>  	struct device_node *np = dev->of_node;
>  	int index;
> -	u64 reg_addr;
> +	u64 reg_addr, fixup_addr;
> +	u64 (*fixup)(struct dw_pcie *pcie, u64 cpu_addr);
>  
>  	/* Look up reg_name address on parent bus */
>  	index = of_property_match_string(np, "reg-names", reg_name);
> @@ -1126,5 +1127,28 @@ resource_size_t dw_pcie_parent_bus_offset(struct dw_pcie *pci,
>  
>  	of_property_read_reg(np, index, &reg_addr, NULL);
>  
> +	fixup = pci->ops->cpu_addr_fixup;
> +	if (fixup) {
> +		fixup_addr = fixup(pci, cpu_phy_addr);
> +		if (reg_addr == fixup_addr) {
> +			dev_warn(dev, "%#010llx %s reg[%d] == %#010llx; %ps is redundant\n",

On second thought, I think this one should be a dev_info(), not a
dev_warn().  We know the *current* devicetree describes the offset
correctly, but there may be other devicetrees that do not describe it,
and we need to keep .cpu_addr_fixup() for those other devicetrees.

So there's nothing the current user can or should do about this.

> +				 cpu_phy_addr, reg_name, index,
> +				 fixup_addr, fixup);
> +		} else {
> +			dev_warn(dev, "%#010llx %s reg[%d] != %#010llx fixed up addr; devicetree is broken\n",
> +				 cpu_phy_addr, reg_name,
> +				 index, fixup_addr);
> +			reg_addr = fixup_addr;
> +		}
> +	} else if (!pci->use_parent_dt_ranges) {
> +		if (reg_addr != cpu_phy_addr) {
> +			dev_warn(dev, "devicetree has incorrect translation; please check parent \"ranges\" property. CPU physical addr %#010llx, parent bus addr %#010llx\n",
> +				 cpu_phy_addr, reg_addr);
> +			return 0;
> +		}
> +	}
> +
> +	dev_info(dev, "%s parent bus offset is %#010llx\n",
> +		 reg_name, cpu_phy_addr - reg_addr);
>  	return cpu_phy_addr - reg_addr;
>  }