linux-kernel - Re: [PATCH v1 2/2] PCI: microchip: rework reg region handing

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Date: Tue, 11 Jun 2024 12:10:54 -0500
From: Bjorn Helgaas <helgaas@...nel.org>
To: Conor Dooley <conor.dooley@...rochip.com>
Cc: conor@...nel.org, Daire McNamara <daire.mcnamara@...rochip.com>,
	Lorenzo Pieralisi <lpieralisi@...nel.org>,
	Krzysztof Wilczyński <kw@...ux.com>,
	Rob Herring <robh@...nel.org>, Bjorn Helgaas <bhelgaas@...gle.com>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>, linux-pci@...r.kernel.org,
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-riscv@...ts.infradead.org
Subject: Re: [PATCH v1 2/2] PCI: microchip: rework reg region handing

On Mon, May 27, 2024 at 10:37:17AM +0100, Conor Dooley wrote:
> The PCI host controller on PolarFire SoC has multiple "instances", each
> with their own bridge and ctrl address spaces. The original binding has
> an "apb" register region, and it is expected to be set to the base
> address of the host controllers register space. Defines in the driver
> were used to compute the addresses of the bridge and ctrl address ranges
> corresponding to instance1. Some customers want to use instance0 however
> and that requires changing the defines in the driver, which is clearly
> not a portable solution.
> 
> The binding has been changed from a single register region to a pair,
> corresponding to the bridge and ctrl regions respectively, so modify the
> driver to read these regions directly from the devicetree rather than
> compute them from the base address of the abp region.
> 
> To maintain backwards compatibility with the existing binding, the
> driver retains code to handle the "abp" reg and computes the base
> address of the bridge and ctrl regions using the defines if it is
> present. reg-names has always been a required property, so this is
> safe to do.

When you update this, can you add something about the objective to the
subject line?  "rework reg region handling" just says "we did
something", but not why or what the benefit is.

The cover letter ("support using either instance 1 or 2") has good
information that could be part of this.

Bjorn