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Subject: Re: [Letux-kernel] [PATCH v5 3/5] misc serdev: Add w2sg0004 (gps receiver) power control driver
From:   "H. Nikolaus Schaller" <hns@goldelico.com>
In-Reply-To: <20180319135418.GL18359@localhost>
Date:   Tue, 20 Mar 2018 15:49:33 +0100
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To:     Johan Hovold <johan@kernel.org>
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Hi Johan,

> Am 19.03.2018 um 14:54 schrieb Johan Hovold <johan@kernel.org>:
>=20
> On Tue, Feb 27, 2018 at 08:32:50AM +0100, H. Nikolaus Schaller wrote:
>> Hi Johan,
>>=20
>>> Am 27.02.2018 um 08:04 schrieb Johan Hovold <johan@kernel.org>:
>>>=20
>>> On Mon, Feb 12, 2018 at 04:26:18PM +0100, Pavel Machek wrote:
>>>> Hi!
>>>>=20
>>>>>> Let's restart this discussion and focus on the main roadblock =
(others
>>>>>> are minor details which can be sorted out later).
>>>>>>=20
>>>>>> If it feels like a hack, the key issue seems to me to be the =
choice of
>>>>>> the API to present the GPS data to user space. Right?
>>>>>=20
>>>>> Or even more fundamentally, does this belong in the kernel at all?
>>>>=20
>>>> Yes, it does.
>>=20
>> Thanks, Pavel for supporting our view.
>>=20
>>>=20
>>> But not necessarily in its current form.
>>=20
>> Is this a "yes after some code fixes"?
>=20
> No, we need some kind of at least rudimentary gps framework even if we
> allow for a raw (NMEA) interface for the time being (possibly
> indefinitely).

Ok, that would be fine if we can get that!

For a minimal set of API I think something like this (following hci_dev) =
would suffice:

struct gps_dev {
	...
	int (*open)(struct gps_dev *gdev);
	int (*close)(struct gps_dev *gdev);
	int (*send)(struct gps_dev *gdev, char *data, int length);
};

int gps_register_dev(struct gps_dev *gdev);
void gps_unregister_dev(struct gps_dev *gdev);
int gps_recv_nmea_chars(struct gps_dev *gdev, char *data, int length);

If that would wrap all creation of some /dev/ttyGPS0 (or however it is =
called),
it would fit our needs for a driver and user-space for our system.

And I would be happy to get rid of creating and registering a =
/dev/ttyGPS0
in the w2sg0004 driver.

Then, the driver will not need to be touched if the GPS framework is =
improved
in some far future (e.g. to provide some additional ioctl for getting =
kalman-filtered
position+heading by doing sensor fusion with some iio-based =
accelerometer/gyro).=20

So I am looking forward to some framework for review and integration =
testing.

BR and thanks,
Nikolaus=