linux-kernel - Re: [PATCH] ARM: /proc/atags: Export also for DT

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Message-ID: <20150128153912.GL28663@atomide.com>
Date:	Wed, 28 Jan 2015 07:39:13 -0800
From:	Tony Lindgren <tony@...mide.com>
To:	Nicolas Pitre <nico@...xnic.net>
Cc:	Pali Rohár <pali.rohar@...il.com>,
	Ivaylo Dimitrov <ivo.g.dimitrov.75@...il.com>,
	Russell King - ARM Linux <linux@....linux.org.uk>,
	Sebastian Reichel <sre@...ian.org>,
	Will Deacon <will.deacon@....com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Pavel Machek <pavel@....cz>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH] ARM: /proc/atags: Export also for DT

* Nicolas Pitre <nico@...xnic.net> [150128 06:37]:
> On Wed, 28 Jan 2015, Pali Rohár wrote:
> 
> > On Wednesday 28 January 2015 01:50:33 Tony Lindgren wrote:
> > > On omaps, the bootrom passes the bootreason in r1 to the
> > > bootloader that can do whatever it wants with it. We could
> > > maybe pass it in the kernel cmdline to the watchdog driver
> > > for user space?
> > > 
> > 
> > Not truth for N900. Bootreason depends on PRM_RSTST omap 
> > register, state of vbat charger pins, time how long was power key 
> > pressed, R&D data stored in CAL partition and other undocumented 
> > registers for omap HS devices. I already tried to implement at 
> > least some subset of it in userspace (or kernel), but it is 
> > impossible because NOLO bootloader clear status of PRM_RSTST 
> > register.
> > 
> > There is also copy of PRM_RSTST register stored at address 
> > 0x4020FFB8 (tracing data) but that address is rewritten (probably 
> > by kernel), so we really cannot implement reading bootreason in 
> > kernel.
> > 
> > But in early stage in uboot it is possible to read 0x4020FFB8 
> > address and get some part of bootreason. But still PRM_RSTST is 
> > not enough!
> > 
> > I would be happy if DT kernel can export /proc/atags file with 
> > ATAGs passed by bootloader. It would be enough for me. In 
> > userspace I can parse content and do what is needed.
> 
> What about defining a DT boot reason property instead?
> Maybe it already exists?  If not, it's something that could certainly be 
> generically used on other platforms too.
> 
> Converting the special ATAG into its standard DT equivalent would then 
> be trivial and much cleaner overall.

Sounds good to me as then we don't have to add any legacy custom
Nokia specific atag. And it won't prevent us from adding a generic
ATAG_BOOTREASON if really needed.

Regards,

Tony
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