linux-kernel - Re: [PATCH RFC NOT TESTED 2/2] PCI: artpec6: Use use_parent_dt_ranges and clean up artpec6_pcie_cpu_addr

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Message-ID: <Z8dem5gBf3xLxSIT@lizhi-Precision-Tower-5810>
Date: Tue, 4 Mar 2025 15:12:11 -0500
From: Frank Li <Frank.li@....com>
To: Bjorn Helgaas <helgaas@...nel.org>
Cc: Jesper Nilsson <jesper.nilsson@...s.com>,
	Lars Persson <lars.persson@...s.com>, Rob Herring <robh@...nel.org>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>,
	Lorenzo Pieralisi <lpieralisi@...nel.org>,
	Krzysztof Wilczyński <kw@...ux.com>,
	Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>,
	Bjorn Helgaas <bhelgaas@...gle.com>, linux-arm-kernel@...s.com,
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-pci@...r.kernel.org
Subject: Re: [PATCH RFC NOT TESTED 2/2] PCI: artpec6: Use
 use_parent_dt_ranges and clean up artpec6_pcie_cpu_addr_fixup()

On Tue, Mar 04, 2025 at 01:08:16PM -0600, Bjorn Helgaas wrote:
> On Tue, Mar 04, 2025 at 12:49:36PM -0500, Frank Li wrote:
> > Remove artpec6_pcie_cpu_addr_fixup() as the DT bus fabric should provide correct
> > address translation. Set use_parent_dt_ranges to allow the DWC core driver to
> > fetch address translation from the device tree.
>
> Shouldn't we be able to detect platforms where DT doesn't describe the
> translation correctly?  E.g., by running .cpu_addr_fixup() on a
> res.start value and comparing the result to the parent_bus_addr()?
> Then we could complain about it if they don't match.

Can't detect because:

There are case, driver have not provide .cpu_addr_fixup, but dts still be
wrong. such as

bus@...00000
{
	ranges = <0xdeaddead 0x1000000 size>;
	pci@...00000 {

		reg = <...>, <0xdeaddead>;
		reg-names = <...>, <config>;
	}

};

above dts can work with current driver, but parent bus address 0xdeaddead
is totally fake address. We can't detect this case because no
.cpu_addr_fixup() at all.

Frank

>
> Bjorn