linux-kernel - Re: [PATCH] Bluetooth: btusb: Configure altsetting for USER

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Message-ID: <925dc4ea-f244-4758-9cab-f3d0439f0b7b@molgen.mpg.de>
Date: Mon, 24 Feb 2025 14:32:30 +0100
From: Paul Menzel <pmenzel@...gen.mpg.de>
To: Hsin-chen Chuang <chharry@...gle.com>
Cc: linux-bluetooth@...r.kernel.org, luiz.dentz@...il.com,
 gregkh@...uxfoundation.org, chromeos-bluetooth-upstreaming@...omium.org,
 Hsin-chen Chuang <chharry@...omium.org>,
 Marcel Holtmann <marcel@...tmann.org>, Ying Hsu <yinghsu@...omium.org>,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Bluetooth: btusb: Configure altsetting for USER_CHANNEL

Dear Hsin-chen,


Am 24.02.25 um 14:06 schrieb Hsin-chen Chuang:

> On Mon, Feb 24, 2025 at 4:42 PM Paul Menzel <pmenzel@...gen.mpg.de> wrote:

>> Am 24.02.25 um 03:24 schrieb Hsin-chen Chuang:
>>> From: Hsin-chen Chuang <chharry@...omium.org>
>>>
>>> Automatically configure the altsetting for USER_CHANNEL when a SCO is
>>> connected or disconnected. This adds support for the USER_CHANNEL to
>>> transfer SCO data over USB transport.
>>
>> Should you re-spin, it’d be great if you elaborated a little more.
>> Especially for the motivation. It’d be also great, if you added how to
>> test this.
> 
> Sure and I'll update this to the commit message in the next patch version.
> 
> The motivation is to enable the HCI_USER_CHANNEL user to send out SCO
> data through USB Bluetooth chips, which is mainly used for
> bidirectional audio transfer (voice call).
> This was not capable because
> - Per Bluetooth Core Spec v5, Vol 4, Part B, 2.1, the corresponding
>    alternate setting should be set based on the air mode in order to
>    transfer SCO data.
> - The Linux Bluetooth HCI_USER_CHANNEL exposes the Bluetooth Host
>    Controller Interface to the user space, which is something above the
>    USB layer. The user space is not able to configure the USB alt while
>    keeping the channel open.
> 
> This patch intercepts the specific packets that indicate the air mode
> change, and configure the alt setting transparently in btusb.
> I tested this patch on ChromeOS devices which are now using the
> Android Bluetooth stack built on top of the HCI_USER_CHANNEL. The USB
> Bluetooth models could work without a customized kernel.

Awesome. Great explanation. It’d be great to have in the commit message. 
I am looking forward to the next iteration.

>>> Fixes: b16b327edb4d ("Bluetooth: btusb: add sysfs attribute to control USB alt setting")
>>> Signed-off-by: Hsin-chen Chuang <chharry@...omium.org>
>>> ---
>>>
>>>    drivers/bluetooth/btusb.c | 224 +++++++++++++++++++++++++++++++-------
>>>    1 file changed, 186 insertions(+), 38 deletions(-)
>>
>> […]

> --
> Best Regards,
> Hsin-chen

Unrelated, and only if you care: Your signature delimiter is missing a 
space at the end [1].


Kind regards,

Paul


[1]: https://en.wikipedia.org/wiki/Signature_block#Standard_delimiter