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.
Registers (BCM59054)
All of them are on MAP0.
PONKEYCTRL1 (0x08)
| Name
|
Bit
|
Description
|
| Reserved/unknown
|
7
|
Reserved/unknown
|
RELEASE_DEB
|
5:3
|
Represents the release debounce.
|
PRESS_DEB
|
2:0
|
Represents the press debounce.
|
PONKEYCTRL2 (0x09)
| Name
|
Bit
|
Description
|
TX1_ACTION
|
7:6
|
TODO
|
TX1_DLY
|
5:3
|
TODO
|
TX1_DEB
|
2:0
|
TODO
|
PONKEYCTRL3 (0x0A)
| Name
|
Bit
|
Description
|
TX2_ACTION
|
7:6
|
TODO
|
TX2_DLY
|
5:3
|
TODO
|
TX2_DEB
|
2:0
|
TODO
|
PONKEYCTRL4 (0x0B)
| Name
|
Bit
|
Description
|
| Reserved/unknown
|
7
|
Reserved/unknown
|
KEY_PAD_LOCK_MODE
|
6
|
TODO
|
KEY_PAD_LOCK
|
5
|
TODO
|
POK_RESTART_EN
|
4
|
TODO
|
| Reserved/unknown
|
3
|
Reserved/unknown
|
POK_WAKUP_DEB
|
2:0
|
TODO
|
PONKEYCTRL5 (0x0C)
| Name
|
Bit
|
Description
|
| Reserved/unknown
|
7:0
|
Reserved/unknown
|
PONKEYCTRL6 (0x0D)
| Name
|
Bit
|
Description
|
| Reserved/unknown
|
7:5
|
Reserved/unknown
|
SMART_RST_DLY
|
4:3
|
TODO
|
SMART_RST_STATUS
|
2
|
TODO
|
SMART_RST_PWR_EN
|
1
|
TODO
|
SMART_RST_EN
|
0
|
TODO
|
PONKEYCTRL7 (0x0E)
| Name
|
Bit
|
Description
|
| Reserved/unknown
|
7:0
|
Reserved/unknown
|
PONKEYCTRL8 (0x0F)
| Name
|
Bit
|
Description
|
TX3_ACTION
|
7:6
|
TODO
|
TX3_DLY
|
5:3
|
TODO
|
TX3_DEB
|
2:0
|
TODO
|