Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933038AbbD0OAH (ORCPT ); Mon, 27 Apr 2015 10:00:07 -0400 Received: from metis.ext.pengutronix.de ([92.198.50.35]:47204 "EHLO metis.ext.pengutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932913AbbD0OAB (ORCPT ); Mon, 27 Apr 2015 10:00:01 -0400 From: Juergen Borleis To: linux-kernel@vger.kernel.org Cc: rtc-linux@googlegroups.com, kernel@pengutronix.de, Alessandro Zummo , linux-arm-kernel@lists.infradead.org, Robert Schwebel Subject: [PATCH 2/6] RTC/i.MX/DryIce: add some background info about the states the machine can be in Date: Mon, 27 Apr 2015 15:59:48 +0200 Message-Id: <1430143192-20667-3-git-send-email-jbe@pengutronix.de> X-Mailer: git-send-email 2.1.4 In-Reply-To: <1430143192-20667-1-git-send-email-jbe@pengutronix.de> References: <1430143192-20667-1-git-send-email-jbe@pengutronix.de> X-SA-Exim-Connect-IP: 2001:67c:670:100:1d::7 X-SA-Exim-Mail-From: jbe@pengutronix.de X-SA-Exim-Scanned: No (on metis.ext.pengutronix.de); SAEximRunCond expanded to false X-PTX-Original-Recipient: linux-kernel@vger.kernel.org Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2440 Lines: 69 Signed-off-by: Juergen Borleis Signed-off-by: Robert Schwebel [rsc: got NDA clearance from Freescale] --- drivers/rtc/rtc-imxdi.c | 43 +++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 43 insertions(+) diff --git a/drivers/rtc/rtc-imxdi.c b/drivers/rtc/rtc-imxdi.c index 0c2a064..6db8d1c 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 */ -- 2.1.4 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/