linux-kernel - Re: [PATCH v1 1/2] Bluetooth: btusb: Indicate Microsoft vendor extension for Intel 9460/9560 and 9160/9260

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Date:   Tue, 24 Mar 2020 19:35:17 +0100
From:   Marcel Holtmann <marcel@...tmann.org>
To:     Alain Michaud <alainmichaud@...gle.com>
Cc:     Joe Perches <joe@...ches.com>,
        Miao-chen Chou <mcchou@...omium.org>,
        Bluetooth Kernel Mailing List 
        <linux-bluetooth@...r.kernel.org>,
        Luiz Augusto von Dentz <luiz.von.dentz@...el.com>,
        Alain Michaud <alainm@...omium.org>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Johan Hedberg <johan.hedberg@...il.com>,
        LKML <linux-kernel@...r.kernel.org>,
        netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH v1 1/2] Bluetooth: btusb: Indicate Microsoft vendor
 extension for Intel 9460/9560 and 9160/9260

Hi Alain,

>>>>>> This adds a bit mask of driver_info for Microsoft vendor extension and
>>>>>> indicates the support for Intel 9460/9560 and 9160/9260. See
>>>>>> https://docs.microsoft.com/en-us/windows-hardware/drivers/bluetooth/
>>>>>> microsoft-defined-bluetooth-hci-commands-and-events for more information
>>>>>> about the extension. This was verified with Intel ThunderPeak BT controller
>>>>>> where msft_vnd_ext_opcode is 0xFC1E.
>>>> []
>>>>>> diff --git a/include/net/bluetooth/hci_core.h b/include/net/bluetooth/hci_core.h
>>>> []
>>>>>> @@ -315,6 +315,10 @@ struct hci_dev {
>>>>>>        __u8            ssp_debug_mode;
>>>>>>        __u8            hw_error_code;
>>>>>>        __u32           clock;
>>>>>> +       __u16           msft_vnd_ext_opcode;
>>>>>> +       __u64           msft_vnd_ext_features;
>>>>>> +       __u8            msft_vnd_ext_evt_prefix_len;
>>>>>> +       void            *msft_vnd_ext_evt_prefix;
>>>> 
>>>> msft is just another vendor.
>>>> 
>>>> If there are to be vendor extensions, this should
>>>> likely use a blank line above and below and not
>>>> be prefixed with msft_
>>> 
>>> there are other vendors, but all of them are different. So this needs to be prefixed with msft_ actually. But I agree that having empty lines above and below makes it more readable.
>> 
>> So struct hci_dev should become a clutter
>> of random vendor extensions?
>> 
>> Perhaps there should instead be something like
>> an array of char at the end of the struct and
>> various vendor specific extensions could be
>> overlaid on that array or just add a void *
>> to whatever info that vendors require.
> I don't particularly like trailing buffers, but I agree we could
> possibly organize this a little better by with a struct.  something
> like:
> 
> struct msft_vnd_ext {
>    bool              supported; // <-- Clearly calls out if the
> extension is supported.
>    __u16           msft_vnd_ext_opcode; // <-- Note that this also
> needs to be provided by the driver.  I don't recommend we have this
> read from the hardware since we just cause an extra redirection that
> isn't necessary.  Ideally, this should come from the usb_table const.

Actually supported == false is the same as opcode == 0x0000. And supported == true is opcode != 0x0000.

>    __u64           msft_vnd_ext_features;
>    __u8             msft_vnd_ext_evt_prefix_len;
>    void             *msft_vnd_ext_evt_prefix;
> };
> 
> And then simply add the struct msft_vnd_ext (and any others) to hci_dev.

Anyway, Lets keep these for now as hci_dev->msft_vnd_ext_*. We can fix this up later without any impact.

Regards

Marcel