FS#55024 - [linux] Enable support for cherry trail PWM controller for backlight brightness control

Attached to Project: Arch Linux
Opened by Daniel Goß (dgoss) - Thursday, 03 August 2017, 10:33 GMT
Last edited by Jan Alexander Steffens (heftig) - Friday, 08 December 2017, 08:37 GMT
Task Type Bug Report
Category Packages: Core
Status Closed
Assigned To Tobias Powalowski (tpowa)
Jan Alexander Steffens (heftig)
Architecture All
Severity Low
Priority Normal
Reported Version
Due in Version Undecided
Due Date Undecided
Percent Complete 100%
Votes 1
Private No

Details

Description:
The current arch linux kernel does not include the necessary code and modules for the cherry trail PWM controller included inside the low power subsystem of the atom SoCs. Kernel 4.12 now contains the necessary patches to detect the cherry trail PWM controller even if DSDT does not explicitly list it. dmesg states "80862288:00: Device [PWM1] is in always present list" on boot. To allow backlight control to work on some cherry trail tablets and notebooks (namely the Asus T102HA) the PWM subsystem of the kernel has to be activated.

I'd like to recommend to enable the following options with the default arch linux kernel to allow backlight brightness control to work out of the box with cherry trail tablets:
CONFIG_PWM=y
CONFIG_PWM_SYSFS=y
CONFIG_PWM_CRC=y
CONFIG_PWM_LPSS=m
CONFIG_PWM_LPSS_PCI=m
CONFIG_PWM_LPSS_PLATFORM=m

I've confirmed that this worked an Asus T102HA with Kernel 4.12.3. All other settings are the default settings for package linux-4.12.3.

Additional info:
* Linux 4.12.3-1

Steps to reproduce:
With the current arch linux kernel configuration the i915 module complains "failed to own the PWM chip" on boot and backlight control does not work. Enabling the configuration options (see above) on kernel 4.12.3 and including pwm-lpss-platform and pwm-lpss-acpi into the initcpio backlight control works as expected.
This task depends upon

Closed by  Jan Alexander Steffens (heftig)
Friday, 08 December 2017, 08:37 GMT
Reason for closing:  Fixed
Additional comments about closing:  4.14.4-2
Comment by canni lecter (elcanni) - Saturday, 02 September 2017, 22:26 GMT
Hello, i have the same problem. I don't know how "including pwm-lpss-platform and pwm-lpss-acpi into the initcpio ".

Thanks!!!
Comment by Daniel Goß (dgoss) - Wednesday, 06 September 2017, 18:24 GMT
In /etc/mkinitcpio.conf you can use the MODULES array to load the specified modules before any other.
Take a look at the wiki for details: https://wiki.archlinux.org/index.php/Mkinitcpio#MODULES

PS: You should use the forum for such requests.
Comment by Raphael Weniger (skweed) - Sunday, 17 September 2017, 18:50 GMT
+1

I can confirm that adding the above mentioned options also works with the tablet Lenovo Yoga 2 8" Windows Edition (Lenovo Yoga 851F).

Comment by Daniel Goß (dgoss) - Wednesday, 06 December 2017, 14:07 GMT
Was there any progress with this? What can I do to support this request?

Building a new kernel on every update to keep the backlight working is really tedious.

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