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

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Message-Id: <0ED606B9-34EB-4FEC-BCC1-19BC60BCF768@jcrosoft.com>
Date:	Thu, 29 Jan 2015 02:00:25 +0800
From:	Jean-Christophe PLAGNIOL-VILLARD <plagnioj@...osoft.com>
To:	Rob Herring <robherring2@...il.com>
Cc:	Jean-Christophe PLAGNIOL-VILLARD <plagnioj@...osoft.com>,
	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>,
	Pali Rohár <pali.rohar@...il.com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH] ARM: /proc/atags: Export also for DT


> On Jan 28, 2015, at 11:57 PM, Rob Herring <robherring2@...il.com> 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…

but if we try to do this generic, where will you store the boot mode

I mean where the SoC boot from

useful to for the Userspace to known where is the bootloader in case of multi boot mode

Best Regards,
J.
> 
> Rob
> 
> _______________________________________________
> linux-arm-kernel mailing list
> linux-arm-kernel@...ts.infradead.org
> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

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