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authorJuergen Borleis <jbe@pengutronix.de>2015-04-27 16:59:48 +0300
committerAlexandre Belloni <alexandre.belloni@free-electrons.com>2015-06-19 21:03:21 +0300
commit3ba3fab765beecd599d8e8e00dc2ed4306518dfd (patch)
treee6f6bb3bc993cca222a72b96185dbc0e65e32a5c /drivers
parente30d31317bb01832379d86826cba1e3dcff78987 (diff)
downloadlinux-3ba3fab765beecd599d8e8e00dc2ed4306518dfd.tar.xz
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')
-rw-r--r--drivers/rtc/rtc-imxdi.c43
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
*/