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

[Wim Van Sebroeck]

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.

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