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

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Date:   Tue, 23 May 2017 15:49:17 +0200
From:   "H. Nikolaus Schaller" <hns@...delico.com>
To:     Rob Herring <robh+dt@...nel.org>
Cc:     Mark Rutland <mark.rutland@....com>,
        Benoît Cousson <bcousson@...libre.com>,
        Tony Lindgren <tony@...mide.com>,
        Russell King <linux@...linux.org.uk>,
        Thierry Reding <treding@...dia.com>,
        Jonathan Cameron <jic23@...nel.org>,
        Maxime Ripard <maxime.ripard@...e-electrons.com>,
        Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        linux-omap <linux-omap@...r.kernel.org>,
        Discussions about the Letux Kernel 
        <letux-kernel@...nphoenux.org>, kernel@...a-handheld.com,
        Marcel Holtmann <marcel@...tmann.org>
Subject: Re: [RFC 0/3] misc: new serdev based drivers for w2sg00x4 GPS module and w2cbw003 wifi/bluetooth

Hi Rob,

> Am 23.05.2017 um 15:10 schrieb Rob Herring <robh+dt@...nel.org>:
> 
> +Marcel

Good!

> 
> On Tue, May 23, 2017 at 7:48 AM, H. Nikolaus Schaller <hns@...delico.com> wrote:
>> Hi Rob,
>> 
>>> Am 23.05.2017 um 14:28 schrieb Rob Herring <robh+dt@...nel.org>:
>>> 
>>> On Tue, May 23, 2017 at 12:43 AM, H. Nikolaus Schaller
>>> <hns@...delico.com> wrote:
>>>> Hi Rob,
>>>> 
>>>>> Am 23.05.2017 um 04:26 schrieb Rob Herring <robh+dt@...nel.org>:
>>>>> 
>>>>> On Sun, May 21, 2017 at 5:44 AM, H. Nikolaus Schaller <hns@...delico.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".

Hm. Well:

root@...ux:~# hciconfig hci0 up
Can't get device info: No such device
root@...ux:~#

I wonder how I can tell hciconfig about the UART port if not by running hciattach /dev/ttyBT0?

> 
>> 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
> hci_mrvl.c.

The w2cb003 has a Marvell WiFi (libertas) but a CSR Bluetooth side.

It has built-in firmware and already talks serial HCI over simple UART right
after power-on. This is why our serdev driver has no firmware download.

> 
>>> 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.
> 
> Okay.
> 
> Rob

BR,
Nikolaus