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

[Akshay Bhat]

Rob,

On 12/28/2015 11:29 AM, Wim Van Sebroeck wrote:
> Hi Tim,
>
> > On Wed, Dec 2, 2015 at 12:54 PM, Tim Harvey <tharvey@xxxxxxxxxxxxx> wrote:
> > > On Wed, Dec 2, 2015 at 11:11 AM, Akshay Bhat <akshay.bhat@xxxxxxxxxxx> wrote:
> > > > 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'm certainly no expert on device-tree policy. I understand your
> > > point, but realize that the driver in question is imx2_wdt.c
> > > (compatible = "fsl,imx21-wdt"). This is an IP block inside the silicon
> > > of only Freescale chips, so its not like a future omap chip would be
> > > using this driver - only fsl devices. So why would it need a 'vendor'
> > > property any more than its other properties?
> > >
> > > Regards,
> > >
> > > Tim
> >
> > Wim,
> >
> > Does the lack of response mean overwhelming approval?
> >
> > I haven't heard any valid complaints - what does it take to get this approved?
> >
> > Regards,
> >
> > Tim
>
> I have no objections against the idea and the code itself.
> But as Guenter pointed out: it would be handy to get feedback from the devicetree maintainers on the above discussion.
>
> Kind regards,
> Wim.

Any suggestions on whether a vendor specific prefix is necessary?

Thanks,
Akshay