netdev - 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 15:32:14 -0400
From:   Alain Michaud <alainmichaud@...gle.com>
To:     Marcel Holtmann <marcel@...tmann.org>
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

On Tue, Mar 24, 2020 at 2:35 PM Marcel Holtmann <marcel@...tmann.org> wrote:
>
> 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.
I was thinking of a more generic way to check if the extension is
supported so the higher level doesn't need to understand that
opcode==0 means it's not supported.  For the android extension for
example, this would be a simple boolean (there isn't any opcodes).
>
> >    __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.
I agree, this doesn't have a whole lot of long term consequences,
although some will want to cherry-pick this to older kernels so if
there is something we can do now, it will reduce burden on some
products.

>
> Regards
>
> Marcel
>