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

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Date:	Wed, 28 Jan 2015 18:18:12 +0100
From:	Pali Rohár <pali.rohar@...il.com>
To:	Rob Herring <robherring2@...il.com>
Cc:	Nicolas Pitre <nico@...xnic.net>,
	Ivaylo Dimitrov <ivo.g.dimitrov.75@...il.com>,
	"Russell King - ARM Linux" <linux@....linux.org.uk>,
	Tony Lindgren <tony@...mide.com>,
	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 16:57:18 Rob Herring wrote:
> On Wed, Jan 28, 2015 at 8:33 AM, Nicolas Pitre 
<nico@...xnic.net> wrote:
> > 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.
> 
> I'm fine with that, but we just need to have a standard kernel
> userspace interface in addition to something like
> /proc/device-tree/bootreason. Perhaps this can be the default
> implementation for the watchdog dev. Someday when we decide DT
> is crap and have a new boot interface, we'll have people
> relying on /proc/device-tree. I hope to be retired when that
> happens...
> 
> Rob

Then what about exporting bootreason as /proc/bootreason?

-- 
Pali Rohár
pali.rohar@...il.com

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