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

[Rob Herring]

On Wed, Jan 28, 2015 at 8:33 AM, Nicolas Pitre <nico@xxxxxxxxxxx> wrote:
> On Wed, 28 Jan 2015, Pali RohÃr 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
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