[Letux-kernel] Letux-4.11-rc and Bluetooth

H. Nikolaus Schaller hns at goldelico.com
Tue Apr 25 21:46:16 CEST 2017

> Am 25.04.2017 um 21:31 schrieb H. Nikolaus Schaller <hns at goldelico.com>:
> Hi,
>> Am 25.04.2017 um 21:05 schrieb Andreas Kemnade <andreas at kemnade.info>:
>> On Tue, 25 Apr 2017 20:02:39 +0200
>> "H. Nikolaus Schaller" <hns at goldelico.com> wrote:
>>> I just realized that we have switched for the serdev driver for GPS
>>> in Letux-4.11-rc.
>>> Since we have a special misc/w2cbw003 driver which similarily
>>> checks for open()/close() on the /dev/tty we have broken
>>> Bluetooth power management...
>>> It is not difficult to fix, just some copy&paste the serdev parts
>>> into the w2cbw003 bluetooth power driver. I will try to do asap.
> Well, the copy&paste part was simple and I have pushed it to the w2sg-serdev branch.
> http://git.goldelico.com/?p=gta04-kernel.git;a=shortlog;h=refs/heads/work/hns/misc/w2sg-serdev
> But it is definitively not enough :(
> The problem is that we have again a man-in-the-middle approach, i.e. on one
> side the serdev interface and on the other a new /dev/tty. This works in
> one direction only. The other is missing because we don't need it for GPS.
> Next, hciattach assumes that it can tamper with the tty port's baud rate, flow
> control etc. So this has to be passed to the serdev.
> Makes a lot of additional glue code which has to be developed :(
> Hm. Maybe a better strategy would be to not open the serdev?
> AFAIR, this should make the /dev/ttyO remain available as standard UART.
> But then we must install some "line discipline" to get notified about the
> open()/close() actions. And I have no idea if the serdev API provides enough
> struct pointers to get up to the pointer where we can install the ldisc.

It seems to be possible through:

struct serdev_controller *ctrl = serdev->ctrl;
struct serport *serport = serdev_controller_get_drvdata(ctrl);
struct tty_struct *tty = serport->tty;

and then

* struct tty_ldisc_ops ops = { .open = open_handler; .close = close_handler; };
* create ldisc
* int tty_register_ldisc(int disc, struct tty_ldisc_ops *new_ldisc)
* tty_set_ldisc(struct tty_struct *tty, int disc)

An unanswered question is where to get the 'disc' number from. Can we
assign it freely? It seems to be an index into an array [0..NR_LDISCS-1]

Other question: does an UART tty already have an ldisc assigned? E.g. one
that handles modem control?

And finally an interesting thing: we can intercept set_termios and get the
additional modem control lines for the RS232 driver (DTR, RING etc.).

> I would even prefer this approach if it is possible... It would be much
> less glue code and would avoid this double copying we have in the w2sg driver.
>> Yes, noticed it also yesterday.
>> BTW:
>> For things like
>> mdbus2 -s org.bluez /org/bluez/hci0 org.bluez.NetworkServer1.Register panu btbr0
>> to work, we also need
>> The former pand commandline tool works without. But it does not play
>> well together with recent bluez.
> I see. Have added it to the defconfig.
> BR,
> Nikolaus
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