RockChip：Boot Mode（二）

一：recovery (key)

在无usb接入情况下，通过按压volume-up键再上电进入recovery模式。

由于loader mode的优先级高于recovery模式，故需要断开usb连接。

* rockchip_dnl_key_pressed():

*

* (1) volume-up key (default)

* (2) menu key (If no rockusb)

*

* It's possible that USB is disabled due to developer needs

* a critial size of u-boot.bin.

*

* Disabling USB makes vbus can't be detected any more, so that

* we add menu key. The events trigger are changed:

*

* - rockusb mode(actually fallback to bootrom mode):

*   "volume-up pressed + vbus=1" replaced with "menu pressed"

* - recovery mode:

*   "volume-up pressed + vbus=0" replaced with "volume-up pressed"

*

* At the most time, USB is enabled and this feature is not applied.

*/