Re: [PATCH v4 1/2] watchdog: imx2_wdt: add external reset support via 'ext-reset-output' dt prop

[Akshay Bhat]

On 11/06/2015 05:02 PM, Guenter Roeck wrote:
> On Fri, Nov 06, 2015 at 11:53:42AM -0800, Tim Harvey wrote:
> > On Thu, Nov 5, 2015 at 2:23 PM, Guenter Roeck <linux@xxxxxxxxxxxx> wrote:
> > > On Thu, Nov 05, 2015 at 04:19:21PM -0500, Akshay Bhat wrote:
> > > > From: Tim Harvey <tharvey@xxxxxxxxxxxxx>
> > > >
> > > > The IMX6 watchdog supports assertion of a signal (WDOG_B) which
> > > > can be pinmux'd to an external pin. This is typically used for boards that
> > > > have PMIC's in control of the IMX6 power rails. In fact, failure to use
> > > > such an external reset on boards with external PMIC's can result in various
> > > > hangs due to the IMX6 not being fully reset [1] as well as the board failing
> > > > to reset because its PMIC has not been reset to provide adequate voltage for
> > > > the CPU when coming out of reset at 800Mhz.
> > > >
> > > > This uses a new device-tree property 'ext-reset-output' to indicate the
> > > > board has such a reset and to cause the watchdog to be configured to assert
> > > > WDOG_B instead of an internal reset both on a watchdog timeout and in
> > > > system_restart.
> > > >
> > > > [1] http://lists.infradead.org/pipermail/linux-arm-kernel/2015-March/333689.html
> > > >
> > > > Cc: Lucas Stach <l.stach@xxxxxxxxxxxxxx>
> > > > Signed-off-by: Tim Harvey <tharvey@xxxxxxxxxxxxx>
> > > > ---
> > > >   .../devicetree/bindings/watchdog/fsl-imx-wdt.txt     |  2 ++
> > > >   drivers/watchdog/imx2_wdt.c                          | 20 ++++++++++++++++++--
> > > >   2 files changed, 20 insertions(+), 2 deletions(-)
> > > >
> > > > diff --git a/Documentation/devicetree/bindings/watchdog/fsl-imx-wdt.txt b/Documentation/devicetree/bindings/watchdog/fsl-imx-wdt.txt
> > > > index 8dab6fd..9b89b3a 100644
> > > > --- a/Documentation/devicetree/bindings/watchdog/fsl-imx-wdt.txt
> > > > +++ b/Documentation/devicetree/bindings/watchdog/fsl-imx-wdt.txt
> > > > @@ -9,6 +9,8 @@ Optional property:
> > >
> > > properties ?
> > >
> > > >   - big-endian: If present the watchdog device's registers are implemented
> > > >     in big endian mode, otherwise in native mode(same with CPU), for more
> > > >     detail please see: Documentation/devicetree/bindings/regmap/regmap.txt.
> > > > +- ext-reset-output: If present the watchdog device is configured to assert its
> > >
> > > Should that have a vendor prefix ? Also, not sure if "-output"
> > > has any real value in the property name. "fsl,external-reset", maybe ?
> >
> > Hi Guenter,
> >
> > I don't see why a vendor prefix is necessary - its a feature of the
> > IMX6 watchdog supported by this driver to be able to trigger an
> > internal chip-level reset and/or an external signal that can be hooked
> > to additional hardware.
> Sounded like vendor specific to me, but then I am not a devicetree maintainer,
> so I am not an authority on the subject.

Devicetree maintainers,

Any thoughts?

Tim,

After looking at all the other watchdog drivers, it does not appear that 
there is any other processor which uses a similar feature. Since imx is 
the only processor that appears to support this feature, it might make 
sense in making this vendor specific. If in the future it is found more 
processors support a similar functionality, it can be revisited and 
moved out from being vendor specific?

> > I started with ext-reset, but it was suggested
> > (http://lists.infradead.org/pipermail/linux-arm-kernel/2015-May/347437.html)
> > to also make it clear that this is an 'output' and not a reset input.
> No problem, as long as you get an Ack from a devicetree maintainer.
>
> Guenter
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