linux-kernel - Re: [PATCH v2 2/3] watchdog: bcm2835: Add poweroff code for the Raspberry Pi

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Date:	Tue, 16 Jun 2015 19:28:43 -0600
From:	Stephen Warren <swarren@...dotorg.org>
To:	Noralf Trønnes <noralf@...nnes.org>
CC:	linux-arm-kernel@...ts.infradead.org, devicetree@...r.kernel.org,
	linux-watchdog@...r.kernel.org,
	linux-rpi-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/3] watchdog: bcm2835: Add poweroff code for the Raspberry
 Pi

On 06/16/2015 03:39 AM, Noralf Trønnes wrote:
> 
> Den 16.06.2015 05:07, skrev Stephen Warren:
>> On 06/13/2015 05:39 AM, Noralf Trønnes wrote:
>>> This adds a new poweroff function to the watchdog driver for the
>>> Raspberry Pi. Currently poweroff/halt results in a reboot.
>>>
>>> The Raspberry Pi firmware uses the RSTS register to know which
>>> partiton to boot from. The partiton value is spread into bits
>>> 0, 2, 4, 6, 8, 10. Partiton 63 is a special partition used by
>>> the firmware to indicate halt.
>>>
>>> The firmware made this change in 19 Aug 2013 and was matched
>>> by the downstream commit:
>>> Changes for new NOOBS multi partition booting from gsh
>> I don't understand why we need a new compatible value here; why not
>> simply modify the existing bcm2835_power_off() function. That is written
>> to do something that's interpreted by the RPi firmware, not something
>> that the bcm2835 HW does.
>>
>> Admittedly the current name is a bit misleading, but fixing that should
>> be a separate change to fixing the implementation to do what the current
>> firmware expects.
> 
> There are other boards that use the BCM2835 and I didn't want to break the
> behaviour for those that use the reference firmware.

We don't support those other board in mainline Linux AFAIK. In other
discussions, Eric Anholt stated that the Roku 2 for example doesn't use
the same firmware (albeit they were derived from the same base a long
way back apparently) so I have no good reason to believe this logic is a
standard across difference bcm2835 devices. Do you know more specific
details?

> Roku 2 device uses
> this soc, and changing bcm2835_power_off() would break support for it.
> ODROID-W also use BCM2835, but this is a Pi clone so I don't know if they
> have matched their firmware behaviour to that of the Pi (admittedly not
> many boards were made, their source of chips went dry).
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