On 4/23/21 5:27 AM, Rafael J. Wysocki wrote:
On Thu, Apr 22, 2021 at 10:31 PM Sowjanya Komatineni
<skomatineni@xxxxxxxxxx> wrote:
Tegra194 and Tegra186 platforms use separate MCE firmware for CPUs which is
in charge of deciding on state transition based on target state, state idle
time, and some other Tegra CPU core cluster states information.
Current PSCI specification don't have function defined for passing runtime
state idle time predicted by governor (based on next events and state target
residency) to ARM trusted firmware.
Presumably that's because this is not a good idea.
Tegra194 and Tegra186 platforms use separate MCE firmware for CPUs.
MCE firmware handles CPU complex power management states entry/exit
based on its background tasks and uses expected wake time of the core to
decide on state transition.
Expected wake time is based on next event and allowed min residency of
the state which governor predicts in kernel which MCE is not aware of.
So need a way to pass this info from kernel through PSCI to TF-A and
TF-A will update this to MCE along with requested state of entry.
For example, When C6 core idle state is requested, MCE notes the time at
which core is likely to wake up. There could be background tasks running
on core which kernel is not aware of.
When those tasks are completed it will check the remaining time against
states crossover thresholds (programmed by ARM trusted FW) to determine
if its still have enough time to enter into C6 state.
While a core is power gates, it could be woken up for background tasks
and put back to power gated state again by MCE based on expected wake
time of the corresponding core.
So, Tegra194/Tegra186 CPU idle support, we need this runtime state
expected wake time predicted by governor to be passed from kernel to TF-A.
Thanks
Sowjanya
A basic design principle of cpuidle is that it should be possible to
use every governor with every driver and the changes in this series
make the platforms in question only work with menu AFAICS.
