linux-kernel - Re: [PATCH 0/2] ARM: Expose Raspberry Pi revision code in /proc/cpuinfo

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Message-ID: <Zo2WB_2szbCLgxNN@probook>
Date: Tue, 9 Jul 2024 21:56:55 +0200
From: J. Neuschäfer <j.neuschaefer@....net>
To: Stefan Wahren <wahrenst@....net>
Cc: Jonathan Neuschäfer <j.neuschaefer@....net>,
	Rob Herring <robh@...nel.org>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>,
	Florian Fainelli <florian.fainelli@...adcom.com>,
	Broadcom internal kernel review list <bcm-kernel-feedback-list@...adcom.com>,
	Ray Jui <rjui@...adcom.com>, Scott Branden <sbranden@...adcom.com>,
	Eric Anholt <eric@...olt.net>, Russell King <linux@...linux.org.uk>,
	devicetree@...r.kernel.org, linux-rpi-kernel@...ts.infradead.org,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/2] ARM: Expose Raspberry Pi revision code in
 /proc/cpuinfo

On Mon, Jul 08, 2024 at 06:14:01PM +0200, Stefan Wahren wrote:
> Hi Jonathan,
>
> Am 08.07.24 um 01:08 schrieb Jonathan Neuschäfer:
> > Raspberry Pi boards have a "revision code", documented here:
> >
> >    https://www.raspberrypi.com/documentation/computers/raspberry-pi.html#new-style-revision-codes
> AFAIK these revision codes mostly refer to the board and not to the CPU.

True.

> The abuse of /proc/cpuinfo has been rejected in the past and from my
> understanding this applies also in this case.

Alright

> > This patch copies what the downstream kernel does and reads it from the
> > devicetree property /system/linux,revision. This enables some software
> > to work as intended on mainline kernels:
> >
> >    https://github.com/hzeller/rpi-rgb-led-matrix/blob/a3eea997a9254b83ab2de97ae80d83588f696387/lib/gpio.cc#L247
> This is a bad example because the application doesn't really care about
> the kernel and directly access the hardware registers via /dev/mem. A
> proper application would use the dedicated userspace API (GPIO Character
> Device or PWM).

Right

> I would bet that the application does not work with the Raspberry Pi 5.

Probably, yeah.


Jonathan