linux-kernel - Re: [PATCH 5/9] drivers: gpio: add QIXIS FPGA GPIO controller

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Message-ID: <af9b69a7-2e8f-4cdd-a3f3-6375ecfe318c@lunn.ch>
Date: Thu, 10 Jul 2025 16:12:08 +0200
From: Andrew Lunn <andrew@...n.ch>
To: Ioana Ciornei <ioana.ciornei@....com>
Cc: devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-gpio@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	Rob Herring <robh@...nel.org>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>,
	Linus Walleij <linus.walleij@...aro.org>,
	Bartosz Golaszewski <brgl@...ev.pl>,
	Shawn Guo <shawnguo@...nel.org>, Michael Walle <mwalle@...nel.org>,
	Lee Jones <lee@...nel.org>, Frank Li <Frank.Li@....com>
Subject: Re: [PATCH 5/9] drivers: gpio: add QIXIS FPGA GPIO controller

> The FPGA does have an ID register that we could verify and match against
> the board type that we expect.
> 
> On the other hand, I am not 100% on board with the idea to check this
> from the GPIO driver which teoretically should only touch its one
> register. Maybe from the parent's driver we could do that and prevent
> the probing of children if things don't match up. But this does prove to
> be complicated since those drivers are simple-mfd (for LS1046AQDS) and
> simple-mfd-i2c (for LX2160ARDB). And I don't think it would be wise to
> add some specific board logic into of/platform.c.

My experience is, DT authors will mess up and put in the wrong
compatible. And the wrong compatible might be enough for it to mostly
work, so you end up with deployed systems with wrong compatibles. It
then becomes difficult to actually extend the use of the compatible,
without causing regressions.

Also, checking will catch putting the wrong bitstream into the FPGA.

So if you can check it, do check it, and return -ENODEV.

   Andrew