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thermal: core: Add a back up thermal shutdown mechanism

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orderly_poweroff is triggered when a graceful shutdown
of system is desired. This may be used in many critical states of the
kernel such as when subsystems detects conditions such as critical
temperature conditions. However, in certain conditions in system
boot up sequences like those in the middle of driver probes being
initiated, userspace will be unable to power off the system in a clean
manner and leaves the system in a critical state. In cases like these,
the /sbin/poweroff will return success (having forked off to attempt
powering off the system. However, the system overall will fail to
completely poweroff (since other modules will be probed) and the system
is still functional with no userspace (since that would have shut itself
off).

However, there is no clean way of detecting such failure of userspace
powering off the system. In such scenarios, it is necessary for a backup
workqueue to be able to force a shutdown of the system when orderly
shutdown is not successful after a configurable time period.

Reported-by: Nishanth Menon <[email protected]>
Signed-off-by: Keerthy <[email protected]>
Acked-by: Eduardo Valentin <[email protected]>
Signed-off-by: Zhang Rui <[email protected]>
This commit is contained in:
Keerthy 2017-04-18 09:59:59 +05:30 • committed by Zhang Rui
commit ef1d87e06a
3 changed files with 91 additions and 0 deletions
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21
Documentation/thermal/sysfs-api.txt
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@ -582,3 +582,24 @@ platform data is provided, this uses the step_wise throttling policy.
This function serves as an arbitrator to set the state of a cooling
device. It sets the cooling device to the deepest cooling state if
possible.
6. thermal_emergency_poweroff:
On an event of critical trip temperature crossing. Thermal framework
allows the system to shutdown gracefully by calling orderly_poweroff().
In the event of a failure of orderly_poweroff() to shut down the system
we are in danger of keeping the system alive at undesirably high
temperatures. To mitigate this high risk scenario we program a work
queue to fire after a pre-determined number of seconds to start
an emergency shutdown of the device using the kernel_power_off()
function. In case kernel_power_off() fails then finally
emergency_restart() is called in the worst case.
The delay should be carefully profiled so as to give adequate time for
orderly_poweroff(). In case of failure of an orderly_poweroff() the
emergency poweroff kicks in after the delay has elapsed and shuts down
the system.
If set to 0 emergency poweroff will not be supported. So a carefully
profiled non-zero positive value is a must for emergerncy poweroff to be
triggered.