linux-kernel - Re: [PATCH] PPS: Restore lost capture-clear option to pps-gpio module.

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Date:	Thu, 9 Apr 2015 12:49:45 -0700
From:	"Gary E. Miller" <gem@...lim.com>
To:	Jan Lübbe <jlu@...gutronix.de>
Cc:	linux-kernel@...r.kernel.org,
	Rodolfo Giometti <giometti@...eenne.com>,
	Ricardo Martin s <rasm@...up.pt>,
	James Nus s <jamesnuss@...ometrics.ca>
Subject: Re: [PATCH] PPS: Restore lost capture-clear option to pps-gpio
 module.

Yo Jan!

On Thu, 09 Apr 2015 15:05:09 +0200
Jan Lübbe <jlu@...gutronix.de> wrote:

> Hi Gary,
> 
> On Do, 2015-04-02 at 12:21 -0700, Gary E. Miller wrote:
> > In the conversion from platform to device tree the capture-clear
> > option was lost.
> > 
> > capture-clear is needed so that time_pps_fetch() will report both
> > edges of each PPS pulse.  Both edges are needed so that userland
> > programs, like gpsd, can autodetect the leading and trailing PPS
> > edges.
> 
> This is intentional. The userspace program can configure which edges
> it wants to capture at runtime.

Yes, on pps-ldisc, but no on pps-gpio.

If you think I am wrong then please show me how I can do that in my
userspace program. I have talked to several experts that could not
figure out how to do so.  They all started with the same assertion as
yours.

The time_pps_setcap() function call will not work to do so because
the PPS_CAPTUREASSERT is locked out before time_pps_getcap().

You can easily verify this with the ppstest program on a Raspberry
Pi running Debian Wheezy using an Adafruit GPS.  

Notice that info->catpure_clear can ONLY be set one place in the entire
driver, and that place is during platform probing.  pps-gpio.c line 110.
No other place.

Without info->capture_clear it is not possible to capture the clear
edge.   Check pps-gpio.c lines 68 and 82.

I would be happy to provide you ssh access to the test platform
if you think you can prove me wrong.  I have test programs I
can show you that demonstrate this.

> Only the polarity
> (assert-falling-edge) is actually determined by the hardware and must
> be described in the device tree.

Now, but when it was a platform driver the capture assert could also be
selected in the platform hardware description.  I'm just trying to
restore lost functionality.

If instead you would be in favor of always allowing capture assert that
would be good as well.

RGDS
GARY
---------------------------------------------------------------------------
Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97701
	gem@...lim.com  Tel:+1(541)382-8588
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