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Subject: Re: HCI Set custom bandwidth for AuriStream SCO codec
From:   Marcel Holtmann <marcel@holtmann.org>
In-Reply-To: <20190708122512.qqfvtm455ltxxg3h@pali>
Date:   Mon, 8 Jul 2019 15:23:06 +0200
Cc:     Pavel Machek <pavel@ucw.cz>,
        Luiz Augusto von Dentz <luiz.dentz@gmail.com>,
        "linux-bluetooth@vger.kernel.org" <linux-bluetooth@vger.kernel.org>,
        Johan Hedberg <johan.hedberg@gmail.com>
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To:     =?utf-8?Q?Pali_Roh=C3=A1r?= <pali.rohar@gmail.com>
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Hi Pali,

>>>>>>> to be honest, I would rather see WBS implementation finally
>>>>>>> reach PA before we start digging into this.
>>>>>> 
>>>>>> First I want to finish improving A2DP codec support in pulseaudio. Later
>>>>>> I can look at HSP/HFP profiles. Ideally it should have modular/plugin
>>>>>> extensible design. So the aim is that adding new codec would be very
>>>>>> simple, without need to hack something related to mSBC/WBC, AuriStream
>>>>>> or any other codec.
>>>>> 
>>>>> Well HSP don't have support for codec negotiation, but yes a modular
>>>>> design is probably recommended.
>>>>> 
>>>>>> But for AuriStream I need to set custom SCO parameters as described
>>>>>> below and currently kernel does not support it. This is why I'm asking
>>>>>> how kernel can export for userspace configuration of SCO parameters...
>>>>> 
>>>>> We can always come up with socket options but we got to see the value
>>>>> it would bring since AuriStream don't look that popular among
>>>>> headsets, at least Ive never seem any device advertising it like
>>>>> apt-X, etc.
>>>> 
>>>> Pali clearly has such device and he is willing to work on it. Surely
>>>> that means it is popular enough to be supported...?
>>> 
>>> Just put AT+CSRSF=0,0,0,0,0,7 to google search and you would see that
>>> not only I have such device...
>>> 
>>> So I would really would like to see that kernel finally stops blocking
>>> usage of this AuriStream codec.
>> 
>> we need to figure out on how we do the kernel API to allow you this specific setting.
> 
> Hi Marcel! Kernel API for userspace should be simple. Just add two
> ioctls for retrieving and setting structure with custom parameters:
> 
>  syncPktTypes = 0x003F
>  bandwidth = 4000
>  max_latency = 16
>  voice_settings = 0x63
>  retx_effort = 2
> 
> Or add more ioctls, one ioctl per parameter. There is already only ioctl
> for voice settings and moreover it is whitelisted only for two values.

it is not that simple actually. Most profiles define a certain set of parameters and then they try to configure better settings and only fallback to a specification defined default as last resort.

>> We have kept is really simple since there was only CVSD and mSBC as of now.
> 
> Seems that custom codecs are already widely used, so it would be great
> it Linux kernel allows to use also other codecs in future without need
> to explicitly whitelist them.

This is an overstatement. I see only one custom codec being used. Unless you have heard from others. However as stated above, I think we need to provide an array of settings that are similar defined to what the HFP spec does. Then we just load the whole set into the kernel.

>> I am also curious on what the assumptions are for the USB driver alternate settings are when using a different codec.
> 
> I did all above tests and kernel changes with USB bluetooth chip which
> is integrated in notebook's combo bt+wifi intel minipci-e card.

Good to know. Since for mSBC in theory they need a new alternate settings that wasn’t really available.

Regards

Marcel