On 07/17/2016 12:24 PM, Wim Van Sebroeck wrote:
Hi Rasmus,
If the driver indicates that the watchdog is running, the framework
should feed it until userspace opens the device, regardless of whether
the driver has set max_hw_heartbeat_ms.
This patch only affects the case where wdd->max_hw_heartbeat_ms is
zero, wdd->timeout is non-zero, the watchdog is not active and the
hardware device is running (*):
- If wdd->timeout is zero, watchdog_need_worker() returns false both
before and after this patch, and watchdog_next_keepalive() is not
called.
- If watchdog_active(wdd), the return value from watchdog_need_worker
is also the same as before (namely, hm && t > hm). Hence in that case,
watchdog_next_keepalive() is only called if hm == max_hw_heartbeat_ms
is non-zero, so the change to min_not_zero there is a no-op.
- If the watchdog is not active and the device is not running, we
return false from watchdog_need_worker just as before.
That leaves the watchdog_hw_running(wdd) && !watchdog_active(wdd) &&
wdd->timeout case. Again, it's easy to see that if
wdd->max_hw_heartbeat_ms is non-zero, we return true from
watchdog_need_worker with and without this patch, and the logic in
watchdog_next_keepalive is unchanged. Finally, if
wdd->max_hw_heartbeat_ms is 0, we used to end up in the
cancel_delayed_work branch, whereas with this patch we end up
scheduling a ping timeout_ms/2 from now.
(*) This should imply that no current kernel drivers are affected,
since the only drivers which explicitly set WDOG_HW_RUNNING are
imx2_wdt.c and dw_wdt.c, both of which also provide a non-zero value
for max_hw_heartbeat_ms. The watchdog core also sets WDOG_HW_RUNNING,
but only when the driver doesn't provide ->stop, in which case it
must, according to Documentation/watchdog/watchdog-kernel-api.txt, set
max_hw_heartbeat_ms.
This isn't completely true. We will have the following in the linux-watchdog
tree:
drivers/watchdog/aspeed_wdt.c: set_bit(WDOG_HW_RUNNING,
&wdt->wdd.status);
drivers/watchdog/dw_wdt.c: set_bit(WDOG_HW_RUNNING, &wdd->status);
drivers/watchdog/dw_wdt.c: set_bit(WDOG_HW_RUNNING, &wdd->status);
drivers/watchdog/imx2_wdt.c: set_bit(WDOG_HW_RUNNING, &wdog->status);
drivers/watchdog/imx2_wdt.c: set_bit(WDOG_HW_RUNNING, &wdog->status);
drivers/watchdog/max77620_wdt.c: set_bit(WDOG_HW_RUNNING,
&wdt_dev->status);
drivers/watchdog/sbsa_gwdt.c: set_bit(WDOG_HW_RUNNING, &wdd->status);
drivers/watchdog/tangox_wdt.c: set_bit(WDOG_HW_RUNNING,
&dev->wdt.status);
I checked the ones that aren't mentioned and aspeed_wdt, max77620_wdt and
sbsa_gwdt.c
also have a non-zero value for max_hw_heartbeat_ms. But tangox_wdt.c doesn't
set it.
This one will need to be looked at closer.
I had a brief look; the tangox_wdt problem is my fault. I overlooked that with
my commit 'watchdog: tangox: Mark running watchdog correctly'.
We have a number of options: Set max_hw_heartbeat_ms in tangox_wdt.c,
accept this patch, or both. I think we should accept this patch.
Thanks,
Guenter
Signed-off-by: Rasmus Villemoes <rasmus.villem...@prevas.dk>
---
drivers/watchdog/watchdog_dev.c | 10 +++++++---
1 file changed, 7 insertions(+), 3 deletions(-)
diff --git a/drivers/watchdog/watchdog_dev.c b/drivers/watchdog/watchdog_dev.c
index 3595cff..14f8a92 100644
--- a/drivers/watchdog/watchdog_dev.c
+++ b/drivers/watchdog/watchdog_dev.c
@@ -92,9 +92,13 @@ static inline bool watchdog_need_worker(struct
watchdog_device *wdd)
* thus is aware that the framework supports generating heartbeat
* requests.
* - Userspace requests a longer timeout than the hardware can handle.
+ *
+ * Alternatively, if userspace has not opened the watchdog
+ * device, we take care of feeding the watchdog if it is
+ * running.
*/
- return hm && ((watchdog_active(wdd) && t > hm) ||
- (t && !watchdog_active(wdd) && watchdog_hw_running(wdd)));
+ return (hm && watchdog_active(wdd) && t > hm) ||
+ (t && !watchdog_active(wdd) && watchdog_hw_running(wdd));
}
static long watchdog_next_keepalive(struct watchdog_device *wdd)
@@ -107,7 +111,7 @@ static long watchdog_next_keepalive(struct watchdog_device
*wdd)
unsigned int hw_heartbeat_ms;
virt_timeout = wd_data->last_keepalive + msecs_to_jiffies(timeout_ms);
- hw_heartbeat_ms = min(timeout_ms, wdd->max_hw_heartbeat_ms);
+ hw_heartbeat_ms = min_not_zero(timeout_ms, wdd->max_hw_heartbeat_ms);
keepalive_interval = msecs_to_jiffies(hw_heartbeat_ms / 2);
if (!watchdog_active(wdd))
--
2.5.0
Kind regards,
Wim.
