linux-kernel - Re: [PATCH v2 0/8] gnss: add new GNSS subsystem

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Message-Id: <598825FD-67A5-4016-BCE8-A50517472B8F@goldelico.com>
Date:   Thu, 31 May 2018 15:33:41 +0200
From:   "H. Nikolaus Schaller" <hns@...delico.com>
To:     Johan Hovold <johan@...nel.org>
Cc:     Richard Cochran <richardcochran@...il.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Andreas Kemnade <andreas@...nade.info>,
        Arnd Bergmann <arnd@...db.de>, Pavel Machek <pavel@....cz>,
        Marcel Holtmann <marcel@...tmann.org>,
        Sebastian Reichel <sebastian.reichel@...labora.co.uk>,
        Tony Lindgren <tony@...mide.com>, linux-kernel@...r.kernel.org,
        devicetree@...r.kernel.org
Subject: Re: [PATCH v2 0/8] gnss: add new GNSS subsystem


> Am 31.05.2018 um 13:47 schrieb Johan Hovold <johan@...nel.org>:
> 
> On Thu, May 31, 2018 at 11:52:18AM +0200, H. Nikolaus Schaller wrote:
>> 
>>> Am 31.05.2018 um 10:52 schrieb Johan Hovold <johan@...nel.org>:
>>> 
>>> On Wed, May 30, 2018 at 07:38:22AM -0700, Richard Cochran wrote:
>>>> On Wed, May 30, 2018 at 12:32:34PM +0200, Johan Hovold wrote:
>>>>> Another possible extension is to add generic 1PPS support.
>>>> 
>>>> There are two possibilities to consider.
>>>> 
>>>> 1. If the PPS causes an interrupt, then it should hook into the PPS
>>>>  subsystem.
>>> 
>>> Registering a PPS child device is what I had in mind for this.
>> 
>> This seems to be duplicating functionality that is already solved by
>> 
>> https://elixir.bootlin.com/linux/v4.17-rc7/source/Documentation/devicetree/bindings/pps/pps-gpio.txt
>> 
>> and
>> 
>> https://elixir.bootlin.com/linux/v4.17-rc7/source/drivers/pps/clients/pps-gpio.c
>> 
>> Or what is bad with just using that?
> 
> Using pps-gpio would not allow you to describe the hardware properly,
> something which, for example, may be needed for power management (e.g.
> to power on the GNSS receiver when the pps device is being accessed).

Yes, that is indeed a very valid reason to do it that way as the pps-gpio
seems to assume an always-on impulse source.

On the other hand it looks as if the pps framework can't tell the
source when to power on/off because it does not notify when it
is being accessed or not:

https://elixir.bootlin.com/linux/v4.17-rc7/source/drivers/pps/pps.c#L305

BR,
Nikolaus