diff options
author | Juergen Borleis <jbe@pengutronix.de> | 2015-04-27 15:59:48 +0200 |
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committer | Alexandre Belloni <alexandre.belloni@free-electrons.com> | 2015-06-19 20:03:21 +0200 |
commit | 3ba3fab765beecd599d8e8e00dc2ed4306518dfd (patch) | |
tree | e6f6bb3bc993cca222a72b96185dbc0e65e32a5c /drivers/rtc/rtc-imxdi.c | |
parent | e30d31317bb01832379d86826cba1e3dcff78987 (diff) |
rtc: imxdi: add some background info about the states the machine can be in
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>
Diffstat (limited to 'drivers/rtc/rtc-imxdi.c')
-rw-r--r-- | drivers/rtc/rtc-imxdi.c | 43 |
1 files changed, 43 insertions, 0 deletions
diff --git a/drivers/rtc/rtc-imxdi.c b/drivers/rtc/rtc-imxdi.c index 056ef6c951ae..63ca52b2029b 100644 --- a/drivers/rtc/rtc-imxdi.c +++ b/drivers/rtc/rtc-imxdi.c @@ -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 */ |