Re: [PATCH RFC] Bluetooth: Add generic support for vendor HCI frames

[Zijun Hu <zijun.hu@oss.qualcomm.com>]

On 7/20/2026 10:30 PM, Luiz Augusto von Dentz wrote:
>> For Qualcomm multi-subsystem BT chips, the transport wire carries both
>> BT-HCI and PERI-HCI frames. PERI is a subsystem on the chip. Take the
>> upcoming QCC2072 support as an example:
>>
>>     Packet type                BT-HCI indicator   PERI-HCI indicator
>>     --------------------------------------------------------------
>>     CMD (Host -> Controller)   0x01                0x31
>>     ACL Data (bidirectional)   0x02                0x32
>>     EVENT (Controller -> Host) 0x04                0x34
> I would say this was fine, but you actuall need to reclassify these to
> 0xff and then use an extra byte for the vendor opcode. Btw, you said
> you could define H4 headers like this? The spec defines either:
> 
> https://www.bluetooth.com/wp-content/uploads/Files/Specification/HTML/Core_v6.3/out/en/host-controller-interface/three-wire-uart-transport-layer.html#UUID-1cf959bb-57a0-e782-4324-a9bc4ee3f134_table-idm13359018144714
> 
> Or
> 
> https://www.bluetooth.com/wp-content/uploads/Files/Specification/HTML/Core_v6.3/out/en/host-controller-interface/uart-transport-layer.html#UUID-83881875-5fbb-c366-400f-055ba726f70e_table-idm13359015052542
> 
Hi Luiz,

Let us label this approach — which multiplexes the vendor indicator under 0xff — Solution A:

virtual HCI_VENDOR_PKT (0xff) + vendor indicator (0x31/0x32/0x34) + body per indicator
I did consider this solution — let us discuss it in the section below.

The PERI-HCI indicators (0x31/0x32/0x34) are defined by the Qualcomm Bluetooth Extensions
specification for the USB (Bulk Serialization mode), H4 UART, and SPI transports. They have
already been deployed in several generations of commercial multi-subsystem BT chips.

> We end up defining vendor 0xff because it is at the end of the range
> which is probably safer.
>

I am not sure that fully holds here:

First, vendors likely reason the same way — "end of range is safer", Take Qualcomm as an example:
it already used 0xfb/0xfc/0xfd/0xfe as internal indicators.

Second, current transport drivers already use 0xff in ways that break that expectation,
as shown below:

1) bpa10x uses 0xff as the wire indicator for HCI_DIAG_PKT (0xf0):
https://elixir.bootlin.com/linux/v7.1/source/drivers/bluetooth/bpa10x.c#L72

2) btmrvl remaps its wire vendor type 0xFE onto 0xff to carry Marvell vendor events:
https://elixir.bootlin.com/linux/v7.1/source/drivers/bluetooth/btmrvl_sdio.c#L797

3) hci_vhci uses it for the handshake that creates the virtual hdev:
https://elixir.bootlin.com/linux/v7.1/source/drivers/bluetooth/hci_vhci.c#L462
https://elixir.bootlin.com/linux/v7.1/source/drivers/bluetooth/hci_vhci.c#L523
>> To generically support vendor HCI frames:
>>
>> - Show them in btmon logs as they appear on the wire.
>> - Allow userspace to send/receive them via HCI_CHANNEL_USER, with a
>>   socket option to control RX, defaulting off to eliminate regression
>>   risk for existing applications.
> We shouldn't need to do this, we should just accept 0xff as the vendor
> packet type and then use the following byte as the real opcode (0x31,
> 0x32, 0x34). Otherwise, if we start accepting vendor packet types
> outside 0xff this will get crowded quickly and could potentially clash
> with future specs.
> 

The indicator is a full u8, the entire [0x10, 0xef] indicator range is currently
unused, and vendor indicators should be deliberately chosen to avoid conflicting with
the BT SIG assignments.

>> - Add hdev->recv_vendor() to handle vendor frames in hci_rx_work() like
>>   BT frame handlers.
>> - Add hci_send_vendor_frame() API similar to existing __hci_cmd_send().
> Encoding/decoding of the frames should be transparent. I'm fine adding
> code to the likes of btmon to decode vendor packets, we already have
> something similar for Intel although that uses a vendor event not a
> vendor packet (both use 0xff, causing the confusion). The user of the
> user channel shall be able to read/write starting with 0xff then
> decode/encode the next byte as the actual vendor opcode.
> 
>> Signed-off-by: Zijun Hu <zijun.hu@oss.qualcomm.com>
>> ---
>> Hi Luiz
>> To address the below concerns you raised on previous
>> discussion, and inspired from your suggestion to add hdev callback:
>>
>> - Not use safer skb helper like skb_pull_data()
>> - It will skip sending to the monitor, making debugging much harder
>>
>> Looking forward to your further comments.
>>
>> Why hdev->is_vendor() instead of multiplexing vendor frames under a
>> virtual HCI_VENDOR_PKT + vendor indicator byte ?
>>
>> 1) The virtual HCI_VENDOR_PKT isn't used by the core itself
>>    currently, and may be removed later.
>> 2) It makes full use of the indicator (hci_skb_pkt_type(skb)) space,
>>    which is large enough to accommodate vendor frames without an
>>    extra layer of nesting inside HCI_VENDOR_PKT.
>> 3) It lets userspace and btmon logs see the exact same frame as it
>>    appears on the wire.

As noted above, I chose is_vendor() over Solution A. My reasoning follows,
for your reference.

1) Userspace sees exactly what is on the wire, in the same form as BT-HCI frames — 
   clear and consistent, as shown below:
  ┌───────┬──────────┬────────────┬────────────┐
  │ Frame │ BT-HCI   │ PERI-HCI   │ PERI-HCI   │
  │       │ existing │ is_vendor()│ Solution A │
  ├───────┼──────────┼────────────┼────────────┤
  │ CMD   │ 0x01 …   │ 0x31 …     │ 0xff 0x31… │
  ├───────┼──────────┼────────────┼────────────┤
  │ ACL   │ 0x02 …   │ 0x32 …     │ 0xff 0x32… │
  ├───────┼──────────┼────────────┼────────────┤
  │ EVENT │ 0x04 …   │ 0x34 …     │ 0xff 0x34… │
  └───────┴──────────┴────────────┴────────────┘
2) is_vendor() puts PERI-HCI on an equal footing with BT-HCI, so userspace and the transport
   driver can reuse the existing BT-HCI path rather than add a separate encode/decode layer —
   less effort on both sides.

Could you please give me a clear direction 
Solution A or is_vendor()?

I need it before I can move forward with the remaining QCC2072 btusb development work.

thank you.