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

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Message-ID: <x2r2xfxrnkihvpoqiamgjmvppverjugp5r4we7lcfpz6jloxzy@7kdfzxiwv2po>
Date: Mon, 24 Mar 2025 23:00:24 +0530
From: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
To: Bjorn Helgaas <helgaas@...nel.org>
Cc: Frank Li <Frank.Li@....com>, Rob Herring <robh@...nel.org>, 
	Saravana Kannan <saravanak@...gle.com>, Jingoo Han <jingoohan1@...il.com>, 
	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.
> 
> [bhelgaas: split debug to separate patch for easier future revert, commit
> log]
> Link: https://lore.kernel.org/r/20250313-pci_fixup_addr-v11-5-01d2313502ab@nxp.com
> Signed-off-by: Frank Li <Frank.Li@....com>
> Signed-off-by: Bjorn Helgaas <bhelgaas@...gle.com>
> ---
>  drivers/pci/controller/dwc/pcie-designware.c | 26 +++++++++++++++++++-
>  drivers/pci/controller/dwc/pcie-designware.h | 13 ++++++++++
>  2 files changed, 38 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/pci/controller/dwc/pcie-designware.c b/drivers/pci/controller/dwc/pcie-designware.c
> index 0a35e36da703..985264c88b92 100644
> --- a/drivers/pci/controller/dwc/pcie-designware.c
> +++ 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",
> +				 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) {

Is this check still valid? 'use_parent_dt_ranges' is only used here for
validation. Moreover, if the fixup is not available, we should be able to
safely return 'cpu_phy_addr - reg_addr' unconditionally.

> +		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);

This info is useless on platforms having no translation between CPU and PCI
controller. The offset will always be 0.

- Mani

-- 
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