[Letux-kernel] w2sg004 woes

H. Nikolaus Schaller hns at goldelico.com
Sun Feb 12 21:18:43 CET 2017

> Am 12.02.2017 um 20:19 schrieb Andreas Kemnade <andreas at kemnade.info>:
> Hi,
> On Sun, 12 Feb 2017 10:11:38 +0100
> "H. Nikolaus Schaller" <hns at goldelico.com> wrote:
>> Hi,
>>> Am 12.02.2017 um 09:43 schrieb Andreas Kemnade
>>> <andreas at kemnade.info>:
>>> Hi,
>>> I just noticed this waring occuring when the gps module is loaded
>>> with a recent kernel.
>>> Maybe someone knows about what is wring.
>> Yes. It comes from the tty/uart layer and our uart-slave patches. It
>> seems that uart_change_pm is not allowed during driver probing. Or
>> some pm isn't initialized at this point. Or something else :)
>> Since this warning does not harm (except for a 200ms boot delay), I
>> did not invest any time to fix it.
>> Anyways, we have to rework the w2sg driver completely to get it
>> upstream by using the new serdev interface. This means that this call
>> sequence will go away completely and we will remove our own fix in
>> the end...
>> There is already a w2sg driver skeleton based on serdev in branch
>> work/hns/misc/w2sg-serdev.
> Does that mean... there is support for advanced serial stuff accepted by
> mainline

yes, it is basically accepted. Especially by the Bluetooth/N900/TiWi
driver people. They seem to have been waiting for long time for such
a feature as well and our solution didn't make them happy.

Something has arrived in linux-next:


> so that we simply can build our serial pm stuff upon it

yes. I think it should work as I have described. The only thing I don't
exactly know is how to correctly handle buffers and block sizes. Serdev
seems to present all bytes it has received while a read() from user space
might not expect that much.

> so that we can finally upstream these things after long years?

Well, this will still lead to debates why we need to create a driver
for this at all since it is a plain serial device. Why it opens another
/dev/tty. Why it needs so complex buffer management etc. Then we must
explain the man-in-the-middle role of the driver for proper power-management.

> I just stumbled upon this message because the gps pm seems to have
> problems on my gta04a4.

Hm. Shouldn't behave differently.

> I wrote some stuff to better analyze power consumption
> and found out nothing suspicious about the gta04a5 hardware
> and musb/twl4030-phy pm seems to work at least under some conditions.
> I will analyze further.

Ok! Please let us know what you find.

I had mixed suspend current measurements with modem voice tests and
maybe the dialling and alsa setup draws more power than needed and
something is/wasn't turned off?


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