linux-kernel - [PATCH 3.2 043/110] watchdog: omap: assert the counter being stopped before reprogramming

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <lsq.1439201551.335009183@decadent.org.uk>
Date:	Mon, 10 Aug 2015 12:12:31 +0200
From:	Ben Hutchings <ben@...adent.org.uk>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:	akpm@...ux-foundation.org, "Guenter Roeck" <linux@...ck-us.net>,
	"Wim Van Sebroeck" <wim@...ana.be>,
	"Uwe Kleine-König" 
	<u.kleine-koenig@...gutronix.de>
Subject: [PATCH 3.2 043/110] watchdog: omap: assert the counter being
 stopped before reprogramming

3.2.71-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Uwe Kleine-König <u.kleine-koenig@...gutronix.de>

commit 530c11d432727c697629ad5f9d00ee8e2864d453 upstream.

The omap watchdog has the annoying behaviour that writes to most
registers don't have any effect when the watchdog is already running.
Quoting the AM335x reference manual:

	To modify the timer counter value (the WDT_WCRR register),
	prescaler ratio (the WDT_WCLR[4:2] PTV bit field), delay
	configuration value (the WDT_WDLY[31:0] DLY_VALUE bit field), or
	the load value (the WDT_WLDR[31:0] TIMER_LOAD bit field), the
	watchdog timer must be disabled by using the start/stop sequence
	(the WDT_WSPR register).

Currently the timer is stopped in the .probe callback but still there
are possibilities that yield to a situation where omap_wdt_start is
entered with the timer running (e.g. when /dev/watchdog is closed
without stopping and then reopened). In such a case programming the
timeout silently fails!

To circumvent this stop the timer before reprogramming.

Assuming one of the first things the watchdog user does is setting the
timeout explicitly nothing too bad should happen because this explicit
setting works fine.

Fixes: 7768a13c252a ("[PATCH] OMAP: Add Watchdog driver support")
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
Reviewed-by: Guenter Roeck <linux@...ck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@...ana.be>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 drivers/watchdog/omap_wdt.c | 7 +++++++
 1 file changed, 7 insertions(+)

--- a/drivers/watchdog/omap_wdt.c
+++ b/drivers/watchdog/omap_wdt.c
@@ -150,6 +150,13 @@ static int omap_wdt_open(struct inode *i
 
 	pm_runtime_get_sync(wdev->dev);
 
+	/*
+	 * Make sure the watchdog is disabled. This is unfortunately required
+	 * because writing to various registers with the watchdog running has no
+	 * effect.
+	 */
+	omap_wdt_disable(wdev);
+
 	/* initialize prescaler */
 	while (__raw_readl(base + OMAP_WATCHDOG_WPS) & 0x01)
 		cpu_relax();

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/