Highly distorted sound / feedback in headphones on kernel 4.17

[sundarnagarajan]

Model: RDP 1130 11.6-inch model
ALSA driver: bytcr_rt5651

Sound over the speakers is OK
The bytcr_rt5651 ALSA driver has software switching between speakers and headphone.
When you switch the sound to headphones (using Sound settings), sound in the headphone is completely distorted and drowned out by a LOUD screech - like feedback

Distributions / kernels tested:

• Ubuntu (standard), Bionic Beaver, kernel 4.17.3
• Ubuntu (standard), Bionic Beaver, kernel 4.16.18 - problem does not occur
• Ubuntu Mate, Bionic Beaver, kernel 4.17.3
• Ubuntu Mate, Bionic Beaver, kernel 4.16.18 - problem does not occur
• xubuntu , Bionic Beaver, kernel 4.17.3
• xubuntu , Bionic Beaver, kernel 4.16.18 - problem does not occur

Analysis:
Possibly a UCM config issue

[sundarnagarajan]

New version of bytcr-rt5651.conf from Hans de Goede checked in Jun-22-2018

New version of HiFi checked in by Hans de Goede checked in Jun-22-2018

With the new UCM config files, problem occurs ONLY on kernel 4.17+. Using new UCM config files, on kernel 4.17, only one output (Speaker) is shown.

[sundarnagarajan]

Have filed issue on Pierre Bossart's Intel UCM github repo