* Nicolas Pitre [off-list ref] [150128 06:37]:

On Wed, 28 Jan 2015, Pali Roh?r wrote:

quoted

On Wednesday 28 January 2015 01:50:33 Tony Lindgren wrote:

quoted

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.

Converting the special ATAG into its standard DT equivalent would then 
be trivial and much cleaner overall.

Sounds good to me as then we don't have to add any legacy custom
Nokia specific atag. And it won't prevent us from adding a generic
ATAG_BOOTREASON if really needed.

Regards,

Tony