linux-kernel - Re: [PATCH RFC NOT TESTED 0/2] PCI: dra7xx: Try to clean up dra7xx_pcie_cpu_addr

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Message-ID: <20250317184427.7wkcr7jwu53r5jog@thinkpad>
Date: Tue, 18 Mar 2025 00:14:27 +0530
From: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
To: Bjorn Helgaas <helgaas@...nel.org>
Cc: Frank Li <Frank.Li@....com>, Tony Lindgren <tony@...mide.com>,
	Rob Herring <robh@...nel.org>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>,
	Vignesh Raghavendra <vigneshr@...com>,
	Siddharth Vadapalli <s-vadapalli@...com>,
	Lorenzo Pieralisi <lpieralisi@...nel.org>,
	Krzysztof Wilczyński <kw@...ux.com>,
	Bjorn Helgaas <bhelgaas@...gle.com>, linux-omap@...r.kernel.org,
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-pci@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH RFC NOT TESTED 0/2] PCI: dra7xx: Try to clean up
 dra7xx_pcie_cpu_addr_fixup()

On Mon, Mar 17, 2025 at 12:30:08PM -0500, Bjorn Helgaas wrote:
> On Thu, Mar 13, 2025 at 11:35:21AM +0530, Manivannan Sadhasivam wrote:
> > On Wed, Mar 05, 2025 at 11:20:21AM -0500, Frank Li wrote:
> > > This patches basic on
> > > https://lore.kernel.org/imx/20250128-pci_fixup_addr-v9-0-3c4bb506f665@nxp.com/
> > > 
> > > I have not hardware to test.
> > > 
> > > Look for driver owner, who help test this and start move forward to remove
> > > cpu_addr_fixup() work.
> > 
> > If you remove cpu_addr_fixup() callback, it will break backwards
> > compatibility with old DTs.
> 
> Do you have any pointers to DTs that will be broken?  Or to commits
> where they were fixed?
> 

Any patch that fixes issues in DT and then makes the required changes in the
driver without accounting for the old DTs will break backwards compatibility.

> > You should fix the existing DTs and continue carrying the callback
> > for a while.
> 
> Any insight into where these existing DTs are used and how long
> they're likely to live?
> 

There is no fixed rule in this afaik. Just like we continue to support old
hardwares, we need to continue supporting old DTs for some time. The best we can
do is provide some warning so that users can update their DTBs. Then we can get
rid of the old DT support in the driver after some time.

That's why I asked Frank to add the warning previously.

- Mani

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