Is there a way to read/write PMIC registers from user space?

Products Support DragonBoard410c
#1

Hi Team,

We are working on a custom board based on apq8016 and Linaro 18.01.

Is there any way we can read/write PMIC registers from the userspace?

Regards,
Parth Y Shah

Disable class-D speaker amplifier when using headphone channels
#2

The pm8916 is connected to the SPMI bus, and not directly mapped to memory. However the pm8916 driver (qcom-spmi-pmi) creates two regmaps used by subdrivers (watchdog, pon…). You can find them exposed in debugfs: /sys/kernel/debug/regmap/0-00 and /sys/kernel/debug/regmap/0-01 respectively slave USID 0 and slave USID 1 as described in the pm8916 hardware register description.

You can read the registers, but not write them, except if you enable it with #define REGMAP_ALLOW_WRITE_DEBUGFS and recompile your kernel. It’s however not recommended to do that in userspace. Then you should be able to write to the register:
e.g. write 0x42 to register 0x0800:

echo -n "0x0800 0x42" > /sys/kernel/debug/regmap/0-00/registers
#3

Thanks Loic, it worked!

#4

Hi Loic,

Is this for Linux only?
In android, this path does not exist.
Is there a way to access to PMIC registers on 410c running Android please?
regards
sk

#5

What Android are you running? Ancient and unsupported qualcomm? Or recent AOSP? If the latter, then it should work the same, since it should be running basically the same kernel.

#6

5.1.1
Last snapshot available on 96board download page (AOSP snapshot 99)

I found a way using this path:
shell@msm8916_64:/sys/kernel/debug/spmi/spmi-0 # echo 0x00000 > address
shell@msm8916_64:/sys/kernel/debug/spmi/spmi-0 # echo 40> count
shell@msm8916_64:/sys/kernel/debug/spmi/spmi-0 # cat data

but I would like confirmation by experts…
regards
sk

#7

That’s ancient and unsupported qualcomm fork of Android. I’d suggest building AOSP for it.
Build instructions are here; Building Android Open Source Project (AOSP) for Dragonboard - 96Boards

#8

ok,

can you give me details about solving this duplicate path plz?

I don’t understand what he was doing to fix that

sk

#9

After you sync the local_manifests, go into that directory and edit the file “linaro.xml” and add these two lines above the lines adding the dragonboard projects;

  <remove-project name="device/linaro/dragonboard" />
  <remove-project name="device/linaro/dragonboard-kernel" />

What those will do is just remove the db845c projects that are causing the path collisions.

You could also try my pinned manifests, which might work for db410c. I haven’t had the chance to work at all on the 410 except just for adding the files to the repository. I’m planning to work on that one after I get the db820c straightened out fully.

And note that despite my focus on automotive, it will create “normal” builds for all targets except “db820c_car”.

#10

thanks man, really appreciate your support.
Regards
sk