RFC Better domain idle from device wakeup patterns

Hello,

I was looking for an option to do better power management for some domains where the devices enter runtime PM in a predictable fashion. For example a display device that sends a vsync interrupt every 16 ms for a 60 Hz panel. These interrupts are not timer interrupts but tend to interrupt periodically to service the workflow and the devices and domains may go back to idle soon after. Two domains are affected by this
- the device's PM domain and the CPU PM domain.

As a first step, I am looking to solve for the device's PM domain idle state (and hopefully solve for the CPU PM domains subsequently). The PM domain could have multiple idle states and/or the enter/exit latencies could be high. In either case, it may not always be beneficial to power off the domain, only to turn it back on before satisfying the idle state residency. When the wakeup is known for the device, we could use that to determine the worthiness of entering a domain idle state. Only the device can tell us when the future event would be and that could change as the usecase changes. Like, when the panel refresh rate increases to 120 Hz. If this information was made available to runtime PM, we could use that in the domain governor to determine a suitable idle state. This is the idea behind these patches.

In the first patch, I am proposing an API for devices to specify their wakeup as a time in the future and in the second patch, I am updating the PM domain governor to use this information to determine the idle state. I have not had a chance to test this out yet, but I wanted to know if I am on the right track.

Would appreciate your thoughts on this.

Thanks,
Lina

Lina Iyer (2):
PM / runtime: register device's next wakeup
PM / Domains: use device's next wakeup to determine domain idle state

 drivers/base/power/domain_governor.c | 87 ++++++++++++++++++++++++++--
 drivers/base/power/runtime.c         | 31 ++++++++++
 include/linux/pm.h                   |  2 +
 include/linux/pm_domain.h            |  1 +
 include/linux/pm_runtime.h           |  1 +
 5 files changed, 116 insertions(+), 6 deletions(-)

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