Mainline:Broadcom Kona/BCM590xx/PONKEY

The BCM590XX PMU can handle a power-on key (the responsible section is nicknamed PONKEY).

Key press detection

When a key is pressed, the internal IRQ for a key press (BCM59054_IRQ_POK_PRESSED/BCM59056_IRQ_PONKEYB_F) is raised; when it is released, the internal IRQ for a key release (BCM59054_IRQ_POK_RELEASED/BCM59056_IRQ_PONKEYB_R) is raised. A driver can interpret these IRQs to toggle a key on/off (in downstream, it's wired up to KEY_POWER by default.

Debounce interval

A debounce interval can be configured independently for button press and release. The debounce values are 3 bits wide and stored in PONKEYCTRL1.

For the BCM59054/BCM59056, the allowed values are 330ns, 1.2ms, 10ms, 50ms, 100ms, 500ms, 1000ms and 2000ms. For the BCM59039/BCM59042/BCM59055, the allowed values are undocumented, but different from BCM59054/56 - 3 is equal to 100ms (whereas it's 50ms on 54/56).

Timer

TODO. Seems like it might be possible to control long-press function using a timer (one of "poweroff", "restart" or "smart reset"). Relevant kernel sources, notably commented out.