[Letux-kernel] uart / w1 woes

Andreas Kemnade andreas at kemnade.info
Mon Sep 24 07:58:28 CEST 2018


Hi,

here is a short summary of issues I know with uarts:
root at gta04:~# cat /sys/bus/platform/devices/4806c000.serial/power/runtime_status 
active
root at gta04:~# cat /sys/bus/platform/devices/4806a000.serial/power/runtime_status 
active

They are both active, without any user of them. This was discussed on linux-omap
if I remember correctly, but I have to check the result.

not lets tell them that they should power down after 3 seconds of non-usage
root at gta04:~# echo 3000 >/sys/bus/platform/devices/4806a000.serial/power/autosuspend_delay_ms 
root at gta04:~# echo 3000 >/sys/bus/platform/devices/4806c000.serial/power/autosuspend_delay_ms

check wether these mechanisms are actually enabled
root at gta04:~# cat /sys/bus/platform/devices/4806a000.serial/power/control             
auto
root at gta04:~# cat /sys/bus/platform/devices/4806c000.serial/power/control 
auto

check the result:
root at gta04:~# cat /sys/bus/platform/devices/4806a000.serial/power/runtime_status 
suspended
root at gta04:~# cat /sys/bus/platform/devices/4806c000.serial/power/runtime_status 
suspended

So what is the effect of this:
We can stop the last user of the CORE_48M_FCLK,
so it can also power down. At least that is the case with no modules loaded.

If I am doing that with the other uarts as well, I can also remove some user of the PER_48M_FCLK.

So what is the effect of this:
I have seen idle currents down to 30mA, without actual system suspend.
And there is a side effect:
omap_hdq stops working, so battery current reading fails. Probably it does 
not declare required clocks/resources properly (also CORE_48M_FCLK but via CORE_12M_FCLK).

So I had to do a bit morecomplicated script, which includes rmmod omap_hdq and
modprobe omap_hdq which omap_hdq also dislikes. For the removal problem of
omap_hdq I have sumbitted a patch. 

Lets hope that the patch is addressed correct. The last commit to omap_hdq
contains things like this:

> Acked-by: Evgeniy Polyakov <zbr at ioremap.net>
> Signed-off-by: Greg Kroah-Hartman <gregkh at linuxfoundation.org>

no Signed-off-by maintainer.

Regards,
Andreas
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