[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 15:10:55 CEST 2017


On Tue, May 23, 2017 at 7:48 AM, H. Nikolaus Schaller <hns at goldelico.com> wrote:
> Hi Rob,
>> Am 23.05.2017 um 14:28 schrieb Rob Herring <robh+dt at kernel.org>:
>> On Tue, May 23, 2017 at 12:43 AM, H. Nikolaus Schaller
>> <hns at goldelico.com> wrote:
>>> Hi Rob,
>>>> Am 23.05.2017 um 04:26 schrieb Rob Herring <robh+dt at kernel.org>:
>>>> 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?
>>> Because we otherwise can't turn on power when /dev/ttyBT0 is opened and turn off when it
>>> is closed. I.e. it should not be powered unless someone does a hciattach /dev/ttyBT0. And it
>>> should be turned off by a killall hciattach.
>> Still, you can do power control within BT HCI drivers.
> We do not use any driver for bluetooth. We just start hciattach on demand.
> And afaik there is no plugin mechanism for adding power control to hciattach.

You don't need hciattach. All userspace has to do for kernel BT
drivers is "hciconfig hci0 up|down".

> Or do you have a link to what you think about?

Look at the nokia BT or TI (HCI_LL) BT drivers. Those both have f/w
downloading and some GPIO controls. Given that this module is based on
Marvell chipset, I'd expect you need to add serdev support to

>> You wouldn't be
>> limited to just open/close, but can handle suspend/resume as well.
> Well, it does not look as if we need more than open/close since suspend/resume
> is already handled by the regulator driver. We just need to keep it powered off
> if there is no user-space client.



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