linux-kernel - Re: char: Add MFGPT driver for the CS5535/CS5536

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Message-ID: <20061127200421.GB4495@cosmic.amd.com>
Date:	Mon, 27 Nov 2006 13:04:21 -0700
From:	"Jordan Crouse" <jordan.crouse@....com>
To:	"Alan" <alan@...rguk.ukuu.org.uk>
cc:	linux-kernel@...r.kernel.org, info-linux@...mail.amd.com
Subject: Re: char: Add MFGPT driver for the CS5535/CS5536

On 22/11/06 22:17 +0000, Alan wrote:
> > The attached driver provides a low-level interface to the block, and 
> > allows for other kernel drivers to use the timers. 
> 
> Three comments
> 
> 2.	There is an RTC timer interface - could you use that interface
> for some of this so its compatible and consistent ?

Do you mean, use the RTC interface itself (i.e. - turn the mfgpt driver
into an RTC driver), or just emulate parts of the RTC interface in the
MFGPT driver.   I would be fine with the second option - the first doesn't
really fit, since the only functionality the RTC and the MFGPT share is
the periodic interrupt feature (which is sub-optimal on RTC anyway).

If the "timer interrupt" feature feels tacked on, thats because it is.
The best use for the MFGPT block is to drive a duty cycle on the
output pin suitable for LEDs and such.  Most Geode customers would use 
it for that purpose.  Running a close second on the usefulness scale is
the watchdog timer - its always nice to have that sort of functionality 
available at the hardware level (and its a double bonus that the watchdog
can be set up to continue running while in suspend).

The interrupt/NMI functionality was added to the hardware for the BIOS to 
use, and we added it to the kernel driver for a sense of completeness.
I personally can't fathom anybody using the timers, and I would gladly 
remove them if nobody else can come up with a realistic usage model.

> 3.	Ditto for a watchdog use - although that would be a separate
> driver using the kernel hooks anyway.

That was the plan - I do have a watchdog driver that I had when I first
wrote the MFGPT driver for a now defunct project.  I should dust it off
and add it in.

Thanks,
Jordan

-- 
Jordan Crouse
Senior Linux Engineer
Advanced Micro Devices, Inc.
<www.amd.com/embeddedprocessors>

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