[Letux-kernel] [RFC 0/3] misc: new serdev based drivers for w2sg00x4 GPS module and w2cbw003 wifi/bluetooth

Rob Herring robh+dt at kernel.org
Tue May 23 04:26:39 CEST 2017

On Sun, May 21, 2017 at 5:44 AM, H. Nikolaus Schaller <hns at goldelico.com> wrote:
> Since our proposed API was not acceptable and the new serdev API has arrived in 4.11 kernels,
> we finally took the challenge to update the w2sg and w2cbw drivers to use the serdev API.
> The approach is to write a "man in the middle" driver which is on one side a serdev client
> which directly controls the UART where the device is connected to and on the other side
> presents a new tty port so that user-space software can talk to the chips as if they would
> directly talk to the UART of the SoC (e.g. ttyO1). This is similar to connecting to a remote
> serial device e.g. through USB (ttyACM) or Bluetooth UART profiles.
> For example gpsd or hciattach expect a /dev/tty they can control (flow control, baud rate
> etc.).

I understand from the prior discussion why you want to pass the data
thru for gps, but why do you need to do that for BT?

> Here is the result of our first hack which is working as a demo on GTA04 devices (and the
> w2cbw driver can also be used to control a GTA04 variant with WL1837).
> Since it is just a demo hack, the code is not yet cleaned up, nor does it completely pass
> check-patch, nor follows 100% the coding styles. And certainly has some bugs.
> The most significant issue is that calling tty_port_register_device() inside of the
> serdev probe() function makes the serdev probe() function to be entered a second
> time. This does not lead to big problems since we currently have minor = 0
> and this makes the second call assume the device is not available.
> But we have no idea why this happens and how it can be prevented.

Johan's fixes may help there, but it is intended to be temporary to
have a separate API for registering tty ports with or without serdev.


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