linux-kernel - Re: [PATCH V1 5/6] watchdog: da9062: DA9062 watchdog driver

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Date:	Wed, 6 May 2015 13:06:31 -0700
From:	Guenter Roeck <linux@...ck-us.net>
To:	"Opensource [Steve Twiss]" <stwiss.opensource@...semi.com>
Cc:	LINUXKERNEL <linux-kernel@...r.kernel.org>,
	LINUXWATCHDOG <linux-watchdog@...r.kernel.org>,
	Wim Van Sebroeck <wim@...ana.be>,
	Alessandro Zummo <a.zummo@...ertech.it>,
	DEVICETREE <devicetree@...r.kernel.org>,
	David Dajun Chen <david.chen@...semi.com>,
	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>,
	LINUXINPUT <linux-input@...r.kernel.org>,
	Lee Jones <lee.jones@...aro.org>,
	Liam Girdwood <lgirdwood@...il.com>,
	Mark Brown <broonie@...nel.org>,
	Mark Rutland <mark.rutland@....com>,
	Pawel Moll <pawel.moll@....com>,
	RTCLINUX <rtc-linux@...glegroups.com>,
	Rob Herring <robh+dt@...nel.org>,
	Samuel Ortiz <sameo@...ux.intel.com>,
	Support Opensource <Support.Opensource@...semi.com>
Subject: Re: [PATCH V1 5/6] watchdog: da9062: DA9062 watchdog driver

On Wed, May 06, 2015 at 04:30:50PM +0000, Opensource [Steve Twiss] wrote:
> 
> On 06 May 2015 17:02 Guenter Roeck wrote:
> 
> > On Wed, May 06, 2015 at 02:54:37PM +0000, Opensource [Steve Twiss] wrote:
> > > On 18 April 2015 16:53 Guenter Roeck wrote:
> > >
> > > Hi Guenter,
> > >
> > > Thanks for your comments.
> > >
> > > > On 04/17/2015 07:23 AM, S Twiss wrote:
> > > > > From: S Twiss <stwiss.opensource@...semi.com>
> > > > >
> > > > > Add watchdog driver support for DA9062
> > > > >
> > > > > Signed-off-by: Steve Twiss <stwiss.opensource@...semi.com>
> > > > >
> > > > Hi Steve,
> > > >
> > > > Key question here is if the da9062 is really so much different to the da9062
> > > > that you can not use the same driver.
> > >
> > > The DA9062 watchdog driver does have some similarities with the DA9063 watchdog
> > > base functionality -- however the watchdog component in the DA9062 chip has more
> > > features yet to be added in software. I do intend to add these other features ...
> > > however, if "not adding them here" is a problem I can drop the DA9062 watchdog
> > > driver from this patch-set until I have time to write in the newer changes.
> > >
> > > > I am especially concerned about the added da9062_reset_watchdog_timer(),
> > > > given the delay it introduces.
> > >
> > > After giving this some thought, I am going to remove this 300ms delay from the
> > > reset_watchdog_timer() function for my next submission attempt. However
> > > I am adding a 300ms delay into the stop() and update_timeout_register() functions
> > > instead.
> > >
> > > The DA9062 watchdog ping (register CONTROL_F) is "windowed" for protection
> > > against spurious writes -- i.e. the ping function cannot be called within a 250ms
> > > time limit or the PMIC will reset. This windowing protection also extends to altering
> > > the timeout scale in the CONTROL_D register -- in which case if the timeout
> > > register is altered and the ping() function is called within the 250ms limit, the
> > > PMIC will reset. The delay is there to stop that from happening.
> > >
> > > I realised my previous patch was over-sanitised: by putting the time delay into the
> > > ping() function I was protecting CONTROL_D in stop() and update_timeout_register(),
> > > but I was being too over-protective of the ping() function. Therefore if there was an
> > > "incorrect trigger signal", the watchdog would not be allowed to fail because the
> > > driver would have filtered out the errors.
> > >
> > Hi Steve,
> > 
> > From your description, it sounds like the protection is only necessary if there
> > was a previous write to the same register(s). If so, it might make sense to
> > record the time of such writes, and only add the delay if necessary, and only
> > for the remainder of the time.
> > 
> > Would this be possible ?
> > 
> 
> Hi Guenter,
> 
> I think so -- sounds like it should be possible.
> Internally, there are several places where the two registers are written in succession.
> Also, I'll have to re-write my tests in several places.
> 
> Probably the best solution would be to defer this watchdog driver for now, and I'll
> re-submit it at a later date once the other parts of the DA9062 driver are [hopefully :)]
> accepted. That way I can concentrate a solid block of time on the re-testing ... this
> is the most time consuming.
> 
Keeping track of the necessary timeout is not mandatory - that was just a
thought. If that would hold you up, just ignore the above and keep going.

> Is that acceptable to you? -- I don't want to lose your existing comments from your
> previous posts, so I will keep track of those changes you have already requested.
> 
Your call, really. I am fine either way.

Guenter
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