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

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Message-Id: <201501281647.34477@pali>
Date:	Wed, 28 Jan 2015 16:47:34 +0100
From:	Pali Rohár <pali.rohar@...il.com>
To:	Tony Lindgren <tony@...mide.com>
Cc:	Nicolas Pitre <nico@...xnic.net>,
	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

On Wednesday 28 January 2015 16:39:13 Tony Lindgren wrote:
> * 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

And what would new atag ATAG_BOOTREASON solve for Nokia N900? 
Nothing.

-- 
Pali Rohár
pali.rohar@...il.com

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