Re: [PATCH v10 04/10] PCI: dwc: Add helper dw_pcie_init_parent_bus_offset()

[Bjorn Helgaas <helgaas@kernel.org>]

On Mon, Mar 10, 2025 at 04:16:42PM -0400, Frank Li wrote:
> From: Bjorn Helgaas <bhelgaas@google.com>
> 
> Set pci->parent_bus_offset based on the parent bus address from the
> "config" (Root complex mode) and "addr_space" (Endpoint mode).
> 
> .cpu_addr_fixup(cpu_phy_addr). (if implemented) should return the parent
> bus address corresponding according to cpu_phy_addr.
> 
> Sets pp->parent_bus_offset, but doesn't use it, so no functional change
> intended yet.
> 
> Add use_parent_dt_ranges to detect some fake bus translation at platform,
> which have not .cpu_addr_fixup(). Set use_parent_dt_ranges true explicitly
> at platform that have .cpu_addr_fixup() and fixed DTB's range. If not one
> report "fake bus translation" for sometime, this flags can be removed
> safely.

> +int dw_pcie_init_parent_bus_offset(struct dw_pcie *pci, const char *reg_name,
> +				   resource_size_t cpu_phy_addr)
> +{
> +	struct device *dev = pci->dev;
> +	struct device_node *np = dev->of_node;
> +	u64 (*fixup)(struct dw_pcie *pcie, u64 cpu_addr);
> +	u64 reg_addr, fixup_addr;
> +	int index;
> +
> +	/* Look up reg_name address on parent bus */
> +	index = of_property_match_string(np, "reg-names", reg_name);
> +
> +	if (index < 0) {
> +		dev_err(dev, "Missed reg-name: %s, Broken DTB file\n", reg_name);
> +		return -EINVAL;
> +	}
> +
> +	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_info(dev, "%#010llx %s reg[%d] == %#010llx; %ps is redundant\n",
> +				 cpu_phy_addr, reg_name, index,
> +				 fixup_addr, fixup);
> +		} else {
> +			dev_warn_once(dev, "%#010llx %s reg[%d] != %#010llx fixed up addr; DT 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_once(dev, "Your DTB try to use fake translation, Please check parent's ranges property,");
> +			return 0;

IIUC the point of this is to catch a DT that describes a non-zero
offset when the driver did not implement .cpu_addr_fixup() and
therefore assumed "reg_addr == cpu_phy_addr".

I guess that makes sense.  But I think we should include both
addresses in the message to help understand the issue.

> +		}
> +	}
> +
> +	pci->parent_bus_offset = cpu_phy_addr - reg_addr;
> +	dev_info(dev, "%s parent bus offset is %#010llx\n",
> +		 reg_name, pci->parent_bus_offset);
> +
> +	return 0;
> +}

> +++ b/drivers/pci/controller/dwc/pcie-designware.h
> @@ -465,6 +466,16 @@ struct dw_pcie {
>  	struct reset_control_bulk_data	core_rsts[DW_PCIE_NUM_CORE_RSTS];
>  	struct gpio_desc		*pe_rst;
>  	bool			suspended;
> +	/*
> +	 * This flag indicates that the vendor driver uses devicetree 'ranges'
> +	 * property to allow iATU to use the Intermediate Address (IA) for
> +	 * outbound mapping. Using this flag also avoids the usage of
> +	 * 'cpu_addr_fixup' callback implementation in the driver.

This part of the comment is now wrong.

> +	 * If use_parent_dt_ranges is false, warning will print if IA is not
> +	 * equal to cpu physical address. Indicate dtb use a fake translation.
> +	 */
> +	bool			use_parent_dt_ranges;
>  };