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rtc: imxdi: add some background info about the states the machine can be in

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Document the i.MX DryIce machine states.

Signed-off-by: Juergen Borleis <jbe@pengutronix.de>
Signed-off-by: Robert Schwebel <rsc@pengutronix.de>
[rsc: got NDA clearance from Freescale]
Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>
This commit is contained in:
Juergen Borleis 2015-04-27 15:59:48 +02:00 committed by Alexandre Belloni
parent e30d31317b
commit 3ba3fab765
1 changed files with 43 additions and 0 deletions
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43
drivers/rtc/rtc-imxdi.c
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@ -129,6 +129,49 @@ struct imxdi_dev {
struct work_struct work;
};
/* Some background:
*
* The DryIce unit is a complex security/tamper monitor device. To be able do
* its job in a useful manner it runs a bigger statemachine to bring it into
* security/tamper failure state and once again to bring it out of this state.
*
* This unit can be in one of three states:
*
* - "NON-VALID STATE"
* always after the battery power was removed
* - "FAILURE STATE"
* if one of the enabled security events has happened
* - "VALID STATE"
* if the unit works as expected
*
* Everything stops when the unit enters the failure state including the RTC
* counter (to be able to detect the time the security event happened).
*
* The following events (when enabled) let the DryIce unit enter the failure
* state:
*
* - wire-mesh-tamper detect
* - external tamper B detect
* - external tamper A detect
* - temperature tamper detect
* - clock tamper detect
* - voltage tamper detect
* - RTC counter overflow
* - monotonic counter overflow
* - external boot
*
* If we find the DryIce unit in "FAILURE STATE" and the TDCHL cleared, we
* can only detect this state. In this case the unit is completely locked and
* must force a second "SYSTEM POR" to bring the DryIce into the
* "NON-VALID STATE" + "FAILURE STATE" where a recovery is possible.
* If the TDCHL is set in the "FAILURE STATE" we are out of luck. In this case
* a battery power cycle is required.
*
* In the "NON-VALID STATE" + "FAILURE STATE" we can clear the "FAILURE STATE"
* and recover the DryIce unit. By clearing the "NON-VALID STATE" as the last
* task, we bring back this unit into life.
*/
/*
* enable a dryice interrupt
*/