linux-kernel - [PATCH 4.4 70/97] rtc: ds1374: wdt: Fix issue with timeout scaling from secs to wdt ticks

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Date:   Fri, 23 Mar 2018 10:54:57 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Moritz Fischer <mdf@...nel.org>,
        Alexandre Belloni <alexandre.belloni@...e-electrons.com>,
        Sasha Levin <alexander.levin@...rosoft.com>
Subject: [PATCH 4.4 70/97] rtc: ds1374: wdt: Fix issue with timeout scaling from secs to wdt ticks

4.4-stable review patch.  If anyone has any objections, please let me know.

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

From: Moritz Fischer <mdf@...nel.org>


[ Upstream commit 453d0744f6c6ca3f9749b8c57c2e85b5b9f52514 ]

The issue is that the internal counter that triggers the watchdog reset
is actually running at 4096 Hz instead of 1Hz, therefore the value
given by userland (in sec) needs to be multiplied by 4096 to get the
correct behavior.

Fixes: 920f91e50c5b ("drivers/rtc/rtc-ds1374.c: add watchdog support")
Signed-off-by: Moritz Fischer <mdf@...nel.org>
Signed-off-by: Alexandre Belloni <alexandre.belloni@...e-electrons.com>
Signed-off-by: Sasha Levin <alexander.levin@...rosoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 drivers/rtc/rtc-ds1374.c |    7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

--- a/drivers/rtc/rtc-ds1374.c
+++ b/drivers/rtc/rtc-ds1374.c
@@ -527,6 +527,10 @@ static long ds1374_wdt_ioctl(struct file
 		if (get_user(new_margin, (int __user *)arg))
 			return -EFAULT;
 
+		/* the hardware's tick rate is 4096 Hz, so
+		 * the counter value needs to be scaled accordingly
+		 */
+		new_margin <<= 12;
 		if (new_margin < 1 || new_margin > 16777216)
 			return -EINVAL;
 
@@ -535,7 +539,8 @@ static long ds1374_wdt_ioctl(struct file
 		ds1374_wdt_ping();
 		/* fallthrough */
 	case WDIOC_GETTIMEOUT:
-		return put_user(wdt_margin, (int __user *)arg);
+		/* when returning ... inverse is true */
+		return put_user((wdt_margin >> 12), (int __user *)arg);
 	case WDIOC_SETOPTIONS:
 		if (copy_from_user(&options, (int __user *)arg, sizeof(int)))
 			return -EFAULT;