[Bug 90075] [BYT LPSS backlight] Acer Aspire Switch 10 backlight control

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=90075

--- Comment #14 from darlor at seznam.cz ---
Created attachment 133201
  --> https://bugs.freedesktop.org/attachment.cgi?id=133201&action=edit
dsdt.dsl from bios version 1.18

Hello again,
just to let you know, even Hans de Goede`s linux-sunxi [1] with a lot of
not-yet-upstreamed patches for baytrail/cherrytrail does not work. Strange
thing is that this kernel supports lpss-pwm for certain devices (accoring Hans`
Hacking Blog), but on Acer Switch 10 dmesg there is:
[drm] Using crystal_cove_wpm pwm-device for backlight control. 

I inserted a lot of debuging printk messages into sunxi, and there is nothing
indicating that lpss should be used for Switch 10. (but maybe I did something
wrong - modules pwm-lpss and pwm-lpss-platform forced to load from initrd.img,
and i915 module loaded later (via modprobe manualy))

In sunxi I find some commits very interesting:
ACPI / LPSS: Only call pwm_add_table() for Bay Trail PWM if PMIC HRV is 2 [2]
mfd: intel_soc_pmic: Differentiate between Bay and Cherry Trail CRC variants
[3]
mfd: intel_soc_pmic: Export separate mfd-cell configs for BYT and CHT [4]
and very very interesting
ACPI / bus: Introduce a list of ids for "always present" devices
"Several Bay / Cherry Trail devices (all of which ship with Windows 10) hide
the LPSS PWM controller in ACPI..."

Maybe Hans De Goede could shed some light on this issue. 

[1] https://github.com/jwrdegoede/linux-sunxi
[2]
https://github.com/jwrdegoede/linux-sunxi/commit/44eb7ab01b1a3bd3d70f623df013c314e8032316
[3]
https://github.com/jwrdegoede/linux-sunxi/commit/118c804aa8ba9be46667cbafa1755c058e47ed77
[4]
https://github.com/jwrdegoede/linux-sunxi/commit/cb63e6df172879b5476ae704c87bd06ba391a1f9
[5]
https://github.com/jwrdegoede/linux-sunxi/commit/b7ecf663c75eed1e764f57281f9508c49c18516e

I`m including dsdt.dsl_ver1.18 from bios versions 1.18 (I was not able to
upgrade to last 1.20 version via W8). Maybe using custom dsdt could work around
this issue, until (if ever) is this issue solved.

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