Linux 3.19: ThinkPad Muting Redone, New Dell Backlight Support, Acer Is Banging
First up, the ThinkPad ACPI driver has been hugely reworked to simplify sound muting. The ThinkPad ACPI driver is now doing software muting rather than the hardware-based muting of sound. ThinkPad laptops commonly have hardware volume controls going back years for muting and volume up/down. The muting is done at the hardware volume control but is a problem as the Linux user-space will also handle the hotkey events and change the state of the other mixer. In the end you can end up in states where the hardware mixer is muted, the software mixer is unmuted, and when hitting the hardware mute key you will just switch states for both mixers.
Instead of increasing the complexity of ALSA to properly address the issue, the special ThinkPad volume controls are being disabled and turned into just changing the state of the software mixer. The ThinkPad mute and volume buttons are then just treated as regular button events and altering the state of the software mixer. Going with this approach also simplifies the ThinkPad ACPI Linux driver.
For Dell laptop users, the platform driver there has new keyboard backlight support. The Toshiba ACPI driver also has new keyboard backlight updates. Beyond the backlight updates, the Toshiba driver also has improvements to hotkey handling.
When it comes to Acer laptop users, the acerhdf Linux kernel driver adds the bang-bang thermal governor and uses it for supported models. This driver also adds support for new Acer models.
Lastly, the HP Accel driver adds support for the HP ZBook 15. The full list of changes can be found via the x86 platform driver pull request.