Re: [PATCH v8 11/11] PCI: imx6: Add i.MX8Q PCIe root complex (RC) support

[Bjorn Helgaas]

[+cc Qianqiang]

On Mon, Jul 29, 2024 at 04:18:18PM -0400, Frank Li wrote:
> From: Richard Zhu <hongxing.zhu@xxxxxxx>
> 
> Implement i.MX8Q (i.MX8QM, i.MX8QXP, and i.MX8DXL) PCIe RC support. While
> the controller resembles that of iMX8MP, the PHY differs significantly.
> Notably, there's a distinction between PCI bus addresses and CPU addresses.
> 
> Introduce IMX_PCIE_FLAG_CPU_ADDR_FIXUP in drvdata::flags to indicate driver
> need the cpu_addr_fixup() callback to facilitate CPU address to PCI bus
> address conversion according to "ranges" property.

> +static u64 imx_pcie_cpu_addr_fixup(struct dw_pcie *pcie, u64 cpu_addr)
> +{
> +	struct imx_pcie *imx_pcie = to_imx_pcie(pcie);
> +	struct dw_pcie_rp *pp = &pcie->pp;
> +	struct resource_entry *entry;
> +	unsigned int offset;
> +
> +	if (!(imx_pcie->drvdata->flags & IMX_PCIE_FLAG_CPU_ADDR_FIXUP))
> +		return cpu_addr;
> +
> +	entry = resource_list_first_type(&pp->bridge->windows, IORESOURCE_MEM);
> +	offset = entry->offset;
> +	return (cpu_addr - offset);
> +}

I'm sure that with enough effort, we could prove "entry" cannot be
NULL here, but I'm not sure I want to spend the effort, and we're
going to end up with more patches like this:

  https://lore.kernel.org/r/20240911125055.58555-1-qianqiang.liu@xxxxxxx

I propose this minor change:

  entry = resource_list_first_type(&pp->bridge->windows, IORESOURCE_MEM);
  if (!entry)
    return cpu_addr;

  return cpu_addr - entry->offset;

I still think we should get rid of the .cpu_addr_fixup() callback if
possible.  But that's a discussion for another day.

Bjorn