[Gta04-owner] 3.2-rc6-gta04 - another week, another rc.

NeilBrown neilb at suse.de
Mon Dec 19 21:21:18 CET 2011

On Mon, 19 Dec 2011 13:06:13 +0100 "Dr. H. Nikolaus Schaller"
<hns at goldelico.com> wrote:

> Hi Neil,
> Am 19.12.2011 um 12:53 schrieb NeilBrown:
> > On Mon, 19 Dec 2011 11:03:40 +0100 "Dr. H. Nikolaus Schaller"
> > <hns at goldelico.com> wrote:
> > 
> >>> 
> >>> I'll have to build myself a uboot ... are there any tricks I need to know, or
> >> 
> >> What do you intend to change?
> > 
> > Possibly nothing - just want to use the latest and want to know that I can
> > build it myself.
> If you have ideas or find issues, please report here:
> http://projects.goldelico.com/p/gta04-uboot/issues/
> U-Boot-bugs are usually easier and faster fixed than in the kernel.
> > I have an idea that it might be good to drop 3V3 for a few milliseconds early
> > in boot to make sure that the GPS is off so that when we toggle the
> > on/off line we can be certain what state it is in.  That would best be done
> > in uboot I think.
> I am not sure if that is possible at all. The 3V3 line is coming from
> a LDO that is a slave of the REGEN signal of the TPS65950. I.e.
> it becomes enabled by hardware. And it can't be turned off because
> there are other chips (e.g. the USB3322) which is not allowed to receive
> 1.8V signals on the inputs if there is no 3V3.

Oh - that's a shame.

Is it safe to turn 3V3 off during suspend or is it meant to stay on the
whole time?

> So I think we have no real chance to bring the GPS into a specific
> state if it isn't there.
> But - there should be a systematic pattern: after 3V3 is turned on,
> it should be in reset state and need exactly one impulse.

Yes ... it should be off on boot and if we make sure to turn it off on reboot
it should still be off on the next boot.  I worry about kernel crashes etc
that might reboot without a clean shutdown, but maybe I'm worrying too much.

I'll probably just assume it is always off a boot and wait until someone
proves me wrong :-)

> If we really want to bring that into a kernel driver I would suggest
> the following: if there is data on the serial port /dev/ttyO0 and no
> user process has opened the file, we can assume that GPS is
> on. We set a flag and just reset a timer of approx. 2 seconds. If
> there is a timeout, we reset the flag assuming that we have to
> switch on. I think this could be encapsulated in a W2SG driver.
> But needs to modify omap-serial to send such a "I did receive data"
> notification. This may make it difficult to get it upstream.
I we had a really good case and a clean design it might be possible, but
maybe it isn't really needed after all.


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