I am requesting that the following presentation/discussion to be added to the media mini-summit agenda. The intent is to do a very short presentation and leave time for discussion.
Linux media power management - problems, challenges and fixes
Media devices can be very complex to support in software - for example, a small USB TV stick is packed with several components providing the functionality to tune, stream analog and/or digital video and audio. Some hybrid devices support both analog, and digital TV tuning capability with or without a remote control capability. A single TV device, which connects to the PC on a USB bus, could have one or more I2C buses internally to implement tuning and remote control features.
On Linux, several individual component drivers come together to provide full functionality on these media devices. For instance, a single digital USB TV stick will have a USB driver that acts as the front-end for several Linux TV media infrastructure components such as: Digital Video Broadcasting (dvb), Audio, and Video4linux (v4l2). Each of these extensions initialize and control their set of registers on the device with the aid of additional tuner and remote control drivers. As you can see, the infrastructure supporting one of these devices is complex and handling suspend/resume within the OS quickly becomes a challenge. It won't come as a too much of a surprise to hear that most media drivers don't handle power management properly. This is due to the lack of a good PM infrastructure inside the media core, as well as driver bugs in their suspend and resume code paths. This work also includes using devres infrastructure work to handle shared media resources such as tuner, demux etc.
In this presentation, we will discuss what is being done to address these issues and also present an overview of PM infrastructure being considered for future kernel releases.
-- Shuah