Re: [PATCH v2 1/3] power: reset: Add Renesas reset driver

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

On Wed, Feb 22, 2017 at 01:35:12PM +0000, Chris Brandt wrote:
> Hello Geert and Guenter,
> 
> On Thursday, February 16, 2017, Guenter Roeck wrote:
> > FWIW, the watchdog subsystem should support that easily, even with 125 ms
> > hardware timeout. We added that capability for that very purpose. That
> > would only fail if the system is stuck with interrupts disabled for more
> > than 125 ms, which seems unlikely. I think the gpio watchdog on some
> > systems has a similar low hardware timeout.
> 
> 
> While I'm going to try that for the RZ/A1, I have a question for you guys
> (or anyone else that has an opinion about end applications)
> 
> 
> If I were going to make a request to the chip designers to make the timeout longer
> for the next RZ/A chip, what would be a good max timeout for common Linux applications?
> 
> Looking through the drivers in the watchdog directly, I see default timeouts of 20,
> 30, 60, and 120 seconds.
> 
30 and 60 are pretty common for default timeouts, though I personally think
they are a bit long. If you want direct HW support, a maximum of 120 seconds
should be sufficient though not really necessary anymore since the core
supports virtual timeouts. A maximum of at least 30 seconds would be needed
if the watchdog is supposed to run at boot time (ie if it is enabled by
ROMMON/BIOS and kept running by the kernel).

Hope this helps,
Guenter