Re: [PATCH v2 1/4] watchdog: renesas-wdt: add driver

[Guenter Roeck <linux@roeck-us.net>]

On Tue, Apr 05, 2016 at 08:25:46AM +0200, fixed-term.Oleksij.Rempel wrote:
> 
> 
> On 04.04.2016 16:08, Guenter Roeck wrote:
> > On Mon, Apr 04, 2016 at 02:36:54PM +0200, Wolfram Sang wrote:
> >>
> >>> we are using it. So it should be implemented in this driver as well,
> >>> if it is not supported by HW, then we will need to use second timer or
> >>> watchdog for pretimeout interrupt.
> >>
> >> As I said, I have no task like this assigned (and no personal interest,
> >> too). So, you'd need to do it yourself, hire me, or request this feature
> >> from Renesas (and hope that they pass the task to me ;)).
> >>
> > Sorry, I lost the context here. 
> > 
> >>> Please correct me if i'm wrong - module parameter is a way to ignore
> >>> kernel config. For same purpose, to disable wdt at runtime "magic 'V'"
> >>> should be used.
> >>
> >> I have to admit that I don't have a specific use-case, I just did
> >> general support as requested. So, I followed the style that basically
> >> every other watchdog driver has this parameter.
> >>
> > I don't understand this one. Unless I am missing something, the module
> > parameter is standard, and magic close by writing 'V' is supported.
> > What is the problem ?
> 
> Sorry it was more about our internal requirements, which are fallowing:
> - WDT is always on. there should be no option to disable it.
> - WDTs can fail, it is proven fact. In our case, worst scenario, failed
> WDT will kill a car battery. This is why we use many watchdogs in one
> system. So, using differently configured WDTs of one SoC is valid use
> case. From this point, module options are kind of sweet but useless or
> harmful.

No one _has_ to use the module parameter. That doesn't mean that it must
not be there - someone else may want it for some reason.

> - pretimout interrupt is not optional - not any more. Some issues are
> wary hard or impossible to reproduce. Pretimout interrupt helped us to
> debug some of them. If WDT hardware can't provide one, we will need to
> mix two watchdogs (one for reset and other for interrupt) or wdt with
> some other hw timer.

Adding pretimeout support should be easy with a follow-up patch.

> 
> May be this requirements can be passed to upstream as well :)

Keep in mind that a specific use case does not and should not mandate
driver implementation details. The driver can support both module parameter
and pretimeout, but none of those has to be used in a specific application.
Important is that the kernel _supports_ your use case, which should be no
problem.

Thanks,
Guenter