Re: [PATCH v3] watchdog: Add watchdog timer support for the WinSystems EBC-C384

From: Guenter Roeck
Date: Mon Jan 25 2016 - 20:58:25 EST

On 01/25/2016 03:36 PM, William Breathitt Gray wrote:
On 01/25/2016 03:42 PM, Guenter Roeck wrote:
On 01/25/2016 11:28 AM, One Thousand Gnomes wrote:
If ask for 299 seconds surely I should get 300 not 240 ?
(Whether to round off or round up is an interesting question for the
middle range - does it go off early or late - I'd have said late but...)

Matter of endless discussion. Some argue that the value should be rounded
up, some argue that it should be rounded down, some argue that it should
be rounded to the closest match. Each camp has its own valid arguments.
I usually leave it up to the driver's author to decide, with a slight
preference to never select a value larger than requested.

I implemented it to round down simply because it was the simplest
solution (i.e. integer truncation). Although I see merit in an
implementation that rounds to the closest valid value, I'll keep the
current implementation for now due to its simplicity; if enough users of
the driver prefer a different implementation, then I'll add it in a
later patch.

Is there no ACPI entry for it ?

Same here. As long as the board is identified, I tend to leave it up
to the driver author to decide _how_ to identify it.

Only question for me would be if the watchdog timer is implemented
in a Super-IO chip, and if so, if it would be possible to use the chip
identification instead of a DMI (or ACPI) entry to instantiate the driver.

I do not believe there is an ACPI entry for it. Interestingly, the
watchdog timer BIOS configuration option for this motherboard is listed
under the Super I/O menu; perhaps this watchdog timer is implemented in
the Super I/O chip.

The manual for this motherboard does not provide much information about
the Super I/O chip (no model number, etc.), and neither sensors-detect
nor superiotool was able to detect it. I've sent an email to the
motherboard company (WinSystems) requesting further information about
the Super I/O chip and whether the watchdog timer is built-in to the
Super I/O chip.

I had a close look at the board pictures in the manual. Looks like there
is a NCT7802Y hardware monitoring chip on the board. This suggests that the
Super-IO chip does probably not implement hardware monitoring. Not that
it helps much to know that, but it reduces the possibilities.

There is also a pretty large Lattice FPGA on the board, which makes it at
least somewhat likely that the functionality is implemented in that FPGA.