Hanging at idle state while working on Linux for Raspberry Pi

Linux developer Stefan Wahren has been working on adding suspend-to-idle (s2idle) support to Raspberry Pi single-board computers. It works and has power-saving benefits, but the downside is that support initially only applied to older Raspberry Pi boards.

Work is underway to enable sleep transitions from suspend to idle to achieve greater power savings during idle times. With this effort, Raspberry Pi suspend and resume can be handled via UART debugging.

Initially, Raspberry Pi suspend-to-idle support was focused on the Broadcom BCM2835 SoC and was tested with Raspberry Pi 1 Model B, Raspberry Pi 3 Model A+, and Raspberry Pi 3 Model B+. The older SoC was initially designed to run in s2idle mode because it is less complex and has sufficient documentation publicly available.

Stefan’s tests showed that the Raspberry Pi running but with idle processors consumed 1.67 W, but in s2idle mode it dropped to 1.33 W. However, there are known issues related to the inability to disable the USB domain and DWC2 hang support.

Details for those interested in this series of LKML patches.