[PATCH] at91sam9_wdt: Allow watchdog to reset device at early boot
boris.brezillon at free-electrons.com
Fri Dec 5 06:12:21 PST 2014
On Fri, 05 Dec 2014 14:57:05 +0200
Timo Kokkonen <timo.kokkonen at offcode.fi> wrote:
> On 27.11.2014 21:00, Boris Brezillon wrote:
> > Hi Timo,
> > Sorry for the late reply.
> > On Fri, 21 Nov 2014 14:23:30 +0200
> > Timo Kokkonen <timo.kokkonen at offcode.fi> wrote:
> >> By default the driver will start a kernel timer which keeps on kicking
> >> the watchdog HW until user space has opened the watchdog
> >> device. Usually this is desirable as the watchdog HW is running by
> >> default and the user space may not have any watchdog daemon running at
> >> all.
> >> However, on production systems it may be mandatory that also early
> >> crashes and lockups will lead to a watchdog reset, even if they happen
> >> before the user space has opened the watchdog device.
> >> To resolve the issue, add a new device tree property
> >> "enable-early-reset" which will prevent the kernel timer from pinging
> >> the watchdog HW on behalf of user space. The default is still to use
> >> kernel timer, but more strict behavior can be enabled via the device
> >> tree property.
> >> Signed-off-by: Timo Kokkonen <timo.kokkonen at offcode.fi>
> >> ---
> >> Documentation/devicetree/bindings/watchdog/atmel-wdt.txt | 4 ++++
> >> drivers/watchdog/at91sam9_wdt.c | 6 +++++-
> >> 2 files changed, 9 insertions(+), 1 deletion(-)
> >> diff --git a/Documentation/devicetree/bindings/watchdog/atmel-wdt.txt b/Documentation/devicetree/bindings/watchdog/atmel-wdt.txt
> >> index f90e294..a0b7b75 100644
> >> --- a/Documentation/devicetree/bindings/watchdog/atmel-wdt.txt
> >> +++ b/Documentation/devicetree/bindings/watchdog/atmel-wdt.txt
> >> @@ -28,6 +28,10 @@ Optional properties:
> >> entering idle state.
> >> - atmel,dbg-halt : Should be present if you want to stop the watchdog when
> >> entering debug state.
> >> +- enable-early-reset : Should be present if you want to let the
> >> + watchdog timer to expire even before user space has opened the
> >> + device. If not set, a kernel timer will keep on pinging the
> >> + watchdog until it is opened.
> > If you want to make this property generic, maybe you should document it
> > in a generic binding doc
> > (Documentation/devicetree/bindings/watchdog/watchdog.txt ?).
> > Once you're at it, maybe you could document the generic timeout-sec
> > property in this file.
> > Moreover, you might want to parse this property in watchdog_core.c and
> > store the information in the watchdog_device struct.
> I gave a little thought about this today and we could maybe have it like
> watchdog_init_timeout() is today. But I can't really think of any
> generic handling for this property, anything else except storing the
> parsed value to a variable in watchdog_device struct. Everything else is
> HW specific, except how we read the variable.. If we had some logic or
> checking for this variable (other than to check it is not negative)
> maybe then it would make sense.
Okay, I'm fine with keeping this DT property parsing out of the core.
> So I could write a patch to document generic watchdog properties in
> Documentation/devicetree/bindings/watchdog/watchdog.txt (anything else
> generic that would go there except timeout-sec and enable-early-reset?)
I'm not sure you and Guenter agreed on the 'early-keepalive-sec'
property (and this one won't be used in atmel driver since you can't
change the timeout once set), so I'd say the timeout-sec and
enable-early-reset are the only common properties for now.
> and change this patch so that it doesn't document anything in
> atmel-wdt.txt as we already have it documented in generic watchdog.txt.
> Sounds good?
Yes, sounds good to me.
Boris Brezillon, Free Electrons
Embedded Linux and Kernel engineering
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