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

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Message-ID: <b1cc367d-6782-4116-b3e7-3dd12e83032e@gmx.net>
Date: Mon, 8 Jul 2024 18:14:01 +0200
From: Stefan Wahren <wahrenst@....net>
To: 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>
Cc: 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

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.
The abuse of /proc/cpuinfo has been rejected in the past and from my
understanding this applies also in this case.
> 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). I would bet that the application does not work with the
Raspberry Pi 5.

Regards
>
> Signed-off-by: Jonathan Neuschäfer <j.neuschaefer@....net>
> ---
> Jonathan Neuschäfer (2):
>        dt-bindings: arm: bcm2835: Specify /system/linux,revision property
>        ARM: bcm2835: Detect system revision
>
>   Documentation/devicetree/bindings/arm/bcm/bcm2835.yaml | 12 ++++++++++++
>   arch/arm/mach-bcm/board_bcm2835.c                      | 11 +++++++++++
>   2 files changed, 23 insertions(+)
> ---
> base-commit: 22a40d14b572deb80c0648557f4bd502d7e83826
> change-id: 20240707-raspi-revision-84dffdfaebce
>
> Best regards,
> --
> Jonathan Neuschäfer <j.neuschaefer@....net>
>