linux-kernel - [PATCH AUTOSEL for 4.9 147/190] rtc: ds1374: wdt: Fix issue with timeout scaling from secs to wdt ticks

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Message-ID: <20180308045810.8041-147-alexander.levin@microsoft.com>
Date:   Thu, 8 Mar 2018 04:59:56 +0000
From:   Sasha Levin <Alexander.Levin@...rosoft.com>
To:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>
CC:     Moritz Fischer <mdf@...nel.org>,
        Alexandre Belloni <alexandre.belloni@...e-electrons.com>,
        Sasha Levin <Alexander.Levin@...rosoft.com>
Subject: [PATCH AUTOSEL for 4.9 147/190] rtc: ds1374: wdt: Fix issue with
 timeout scaling from secs to wdt ticks

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>
---
 drivers/rtc/rtc-ds1374.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/drivers/rtc/rtc-ds1374.c b/drivers/rtc/rtc-ds1374.c
index 3b3049c8c9e0..5b5bc7dc3a1c 100644
--- a/drivers/rtc/rtc-ds1374.c
+++ b/drivers/rtc/rtc-ds1374.c
@@ -527,6 +527,10 @@ static long ds1374_wdt_ioctl(struct file *file, unsigned int cmd,
 		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 *file, unsigned int cmd,
 		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;
-- 
2.14.1