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

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Message-ID: <20150128180322.GA16868@amd>
Date:	Wed, 28 Jan 2015 19:03:22 +0100
From:	Pavel Machek <pavel@....cz>
To:	Rob Herring <robherring2@...il.com>
Cc:	Nicolas Pitre <nico@...xnic.net>,
	Pali Rohár <pali.rohar@...il.com>,
	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>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH] ARM: /proc/atags: Export also for DT

On Wed 2015-01-28 09:57:18, 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...

Huh. Who thought putting device-tree into /proc was good idea? That
should have gone to /sys, as it is not process related...

Anyway, bootreason does not depend on device-tree, so it should not be
in device-tree specific subdirectory.
									Pavel
-- 
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