On 01/20/2018 08:04 AM, PrasannaKumar Muralidharan wrote:

Hi Guenter,

On 20 January 2018 at 21:15, Guenter Roeck [off-list ref] wrote:

quoted

On 01/19/2018 11:31 PM, PrasannaKumar Muralidharan wrote:

quoted

Hi Paul,

On 30 December 2017 at 19:21, Paul Cercueil [off-list ref] wrote:

quoted

The watchdog driver can restart the system by simply configuring the
hardware for a timeout of 0 seconds.

Signed-off-by: Paul Cercueil <redacted>
Reviewed-by: Guenter Roeck <redacted>
---
   drivers/watchdog/jz4740_wdt.c | 9 +++++++++
   1 file changed, 9 insertions(+)

   v2: No change

diff --git a/drivers/watchdog/jz4740_wdt.c

b/drivers/watchdog/jz4740_wdt.c
index 92d6ca8ceb49..fa7f49a3212c 100644

--- a/drivers/watchdog/jz4740_wdt.c
+++ b/drivers/watchdog/jz4740_wdt.c

@@ -130,6 +130,14 @@ static int jz4740_wdt_stop(struct watchdog_device

*wdt_dev)
          return 0;
   }

+static int jz4740_wdt_restart(struct watchdog_device *wdt_dev,
+                             unsigned long action, void *data)
+{
+       wdt_dev->timeout = 0;
+       jz4740_wdt_start(wdt_dev);
+       return 0;
+}
+
   static const struct watchdog_info jz4740_wdt_info = {
          .options = WDIOF_SETTIMEOUT | WDIOF_KEEPALIVEPING |
WDIOF_MAGICCLOSE,
          .identity = "jz4740 Watchdog",

@@ -141,6 +149,7 @@ static const struct watchdog_ops jz4740_wdt_ops = {
          .stop = jz4740_wdt_stop,
          .ping = jz4740_wdt_ping,
          .set_timeout = jz4740_wdt_set_timeout,
+       .restart = jz4740_wdt_restart,
   };

   #ifdef CONFIG_OF
--

2.11.0

Noticed that min_timeout of the watchdog device is set to 1 but this
function calls start with timeout set to 0. Even though this works I
feel it is better to set min_timeout to 0.

No. That would be wrong. If you want to be pedantic, write a new function
__jz4740_wdt_set_timeout(u16 clock_div, u16 timeout_value) and call it
instead, but don't mess with min_timeout.

Guenter

What is the effect of changing min_timeout? I could see only
validation checks with it.

Let me ask you - you want to let userspace set a timeout of 0, which would
effectively reboot the system through the backdoor. Why ?

Guenter
--
To unsubscribe from this list: send the line "unsubscribe linux-watchdog" in
the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html