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

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Date:	Mon, 25 Jan 2016 18:36:56 -0500
From:	William Breathitt Gray <vilhelm.gray@...il.com>
To:	Guenter Roeck <linux@...ck-us.net>,
	One Thousand Gnomes <gnomes@...rguk.ukuu.org.uk>
Cc:	wim@...ana.be, linux-watchdog@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] watchdog: Add watchdog timer support for the
 WinSystems EBC-C384

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.                                                          

William Breathitt Gray