linux-kernel - Re: [PATCH] Bluetooth: hci_bcm: Configure SCO routing automatically

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Date:   Mon, 11 Jun 2018 20:19:04 +0200
From:   Marcel Holtmann <marcel@...tmann.org>
To:     Rob Herring <robh+dt@...nel.org>
Cc:     Attila Tőkés <attitokes@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Mark Rutland <mark.rutland@....com>,
        Johan Hedberg <johan.hedberg@...il.com>,
        Artiom Vaskov <velemas@...il.com>,
        netdev <netdev@...r.kernel.org>,
        devicetree <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "open list:BLUETOOTH DRIVERS" <linux-bluetooth@...r.kernel.org>
Subject: Re: [PATCH] Bluetooth: hci_bcm: Configure SCO routing automatically

Hi Rob,

>>>>>> Added support to automatically configure the SCO packet routing at the
>>>>>> device setup. The SCO packets are used with the HSP / HFP profiles, but in
>>>>>> some devices (ex. CYW43438) they are routed to a PCM output by default. This
>>>>>> change allows sending the vendor specific HCI command to configure the SCO
>>>>>> routing. The parameters of the command are loaded from the device tree.
>>>>> 
>>>>> Please wrap your commit msg.
>>>> 
>>>> 
>>>> Sure.
>>>>> 
>>>>> 
>>>>>> 
>>>>>> Signed-off-by: Attila Tőkés <attitokes@...il.com>
>>>>>> ---
>>>>>> .../bindings/net/broadcom-bluetooth.txt       |  7 ++
>>>>> 
>>>>> Please split bindings to separate patch.
>>>> 
>>>> 
>>>> Ok, I will split this in two.
>>>>> 
>>>>> 
>>>>> 
>>>>> 
>>>>>> drivers/bluetooth/hci_bcm.c                   | 72 +++++++++++++++++++
>>>>>> 2 files changed, 79 insertions(+)
>>>>>> 
>>>>>> diff --git
>>>>>> a/Documentation/devicetree/bindings/net/broadcom-bluetooth.txt
>>>>>> b/Documentation/devicetree/bindings/net/broadcom-bluetooth.txt
>>>>>> index 4194ff7e..aea3a094 100644
>>>>>> --- a/Documentation/devicetree/bindings/net/broadcom-bluetooth.txt
>>>>>> +++ b/Documentation/devicetree/bindings/net/broadcom-bluetooth.txt
>>>>>> @@ -21,6 +21,12 @@ Optional properties:
>>>>>> - clocks: clock specifier if external clock provided to the controller
>>>>>> - clock-names: should be "extclk"
>>>>>> 
>>>>>> + SCO routing parameters:
>>>>>> + - sco-routing: 0-3 (PCM, Transport, Codec, I2S)
>>>>>> + - pcm-interface-rate: 0-4 (128 Kbps - 2048 Kbps)
>>>>>> + - pcm-frame-type: 0 (short), 1 (long)
>>>>>> + - pcm-sync-mode: 0 (slave), 1 (master)
>>>>>> + - pcm-clock-mode: 0 (slave), 1 (master)
>>>>> 
>>>>> Are these Broadcom specific? Properties need either vendor prefix or
>>>>> to be documented in a common location. I think these look like the
>>>>> latter.
>>>> 
>>>> 
>>>> These will be used as parameters of a vendor specific (Broadcom/Cypress)
>>>> command configuring the SCO packet routing. See the Write_SCO_PCM_Int_Param
>>>> command from: http://www.cypress.com/file/298311/download.
>>> 
>>> The DT should just describe how the h/w is hooked-up. What the s/w has
>>> to do based on that is the driver's problem which is certainly
>>> vendor/chip specific, but that is all irrelevant to the binding.
>>> 
>>>> What would be the property names with a Broadcom / Cypress vendor prefix?
>>>> 
>>>>   brcm,sco-routing
>>>>   brcm,pcm-interface-rate
>>>>   brcm,pcm-frame-type
>>>>   brcm,pcm-sync-mode
>>>>   brcm,pcm-clock-mode
>>>> 
>>>> ?
>>> 
>>> Yes.
>> 
>> we can do this. However all pcm-* are optional if you switch the HCI transport. And sco-routing should default to HCI if that is not present. Meaning a driver should actively trying to change this. Nevertheless, it would be good if a driver reads the current settings.
>> 
>> In theory we could make sco-routing generic, but so many vendors have different modes, that we better keep this vendor specific.
> 
> Even if vendor specific, the properties for not HCI transport case are
> still incomplete IMO.
> 
> By modes, you mean PCM vs. I2S and all the flavors of timings you can
> have within those or something else? For the former, that's often
> going to be a process of solving what each end support and if that
> doesn't work, then IIRC we already have properties for setting
> modes/timing. All the same issues exist with audio codecs and this is
> really not any different.

this is what Broadcom uses to configure their PCM transport. So I think for now, we make them brcm, specific and see how that goes. We can always generalize them later if enough chip manufactures provide support for it.

Regards

Marcel