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

Jean-Christophe PLAGNIOL-VILLARD
2015-01-29T01:07:24Z

> On Jan 28, 2015, at 11:57 PM, Rob Herring <robherring2@gmail.com> wrote:
>
> On Wed, Jan 28, 2015 at 8:33 AM, Nicolas Pitre <nico@fluxnic.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
>
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