On Fri, Feb 07, 2014 at 05:38:09AM -0800, Guenter Roeck wrote: > On 02/07/2014 02:40 AM, Ezequiel Garcia wrote: > > On Thu, Feb 06, 2014 at 06:02:56PM -0800, Guenter Roeck wrote: > >> On 02/06/2014 09:20 AM, Ezequiel Garcia wrote: > >>> Having the watchdog initially fully stopped is important to avoid > >>> any spurious watchdog triggers, in case the registers are not in > >>> its reset state. > >>> > >>> Reviewed-by: Guenter Roeck <linux@xxxxxxxxxxxx> > >>> Tested-by: Sebastian Hesselbarth <sebastian.hesselbarth@xxxxxxxxx> > >>> Tested-by: Willy Tarreau <w@xxxxxx> > >>> Signed-off-by: Ezequiel Garcia <ezequiel.garcia@xxxxxxxxxxxxxxxxxx> > >>> --- > >>> drivers/watchdog/orion_wdt.c | 3 +++ > >>> 1 file changed, 3 insertions(+) > >>> > >>> diff --git a/drivers/watchdog/orion_wdt.c b/drivers/watchdog/orion_wdt.c > >>> index 6746033..2dbeee9 100644 > >>> --- a/drivers/watchdog/orion_wdt.c > >>> +++ b/drivers/watchdog/orion_wdt.c > >>> @@ -142,6 +142,9 @@ static int orion_wdt_probe(struct platform_device *pdev) > >>> orion_wdt.max_timeout = wdt_max_duration; > >>> watchdog_init_timeout(&orion_wdt, heartbeat, &pdev->dev); > >>> > >>> + /* Let's make sure the watchdog is fully stopped */ > >>> + orion_wdt_stop(&orion_wdt); > >>> + > >> > >> Actually we just had that in another driver, and I stumbled over it there. > >> > >> Problem with stopping the watchdog in probe unconditionally is that you can > >> use it to defeat nowayout: unload the module, then load it again, > >> and the watchdog is stopped even if nowayout is true. > >> > > > > Hm... I see. > > > >> Is this really what you want ? Or, in other words, what is the problem > >> you are trying to solve ? > >> > > > > Well, this is related to the discussion about the bootloader not > > reseting the watchdog properly, provoking spurious watchdog triggering. > > > > Jason Gunthorpe explained [1] that we needed a particular sequence: > > > > 1. Disable WDT > > 2. Clear bridge > > 3. Enable WDT > > > > We added the irq handling to satisfy (2), and the watchdog stop for (1). > > > > The watchdog stop was agreed specifically [2]. > > > > Ideas? > > > > Other drivers assume that if the watchdog is running, it is supposed > to be running. The more common approach in such cases is to ping the > watchdog once to give userspace more time to get ready, but leave > it enabled. So you could check if the watchdog is enabled, and if > it was enabled re-enable it after initialization is complete > (and maybe log a message stating that the watchdog is enabled). > > If you don't want to do that, and if you are defeating nowayout > on purpose to fix a problem with a broken bootloader, > you should at least put in comment describing the problem you are > trying to solve, and that you accept breaking nowayout with your fix. > I'm not fond of not having "nowayout" option on our driver, given I'm sure it's a watchdog feature for a good reason. On the other side, I can't see how can we distinguish a previously and explicitly enabled watchdog, from a spurious enable by broken bootloader. Jason, what do you say? -- Ezequiel García, Free Electrons Embedded Linux, Kernel and Android Engineering http://free-electrons.com -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
