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From:   Miao-chen Chou <mcchou@chromium.org>
Date:   Tue, 24 Mar 2020 22:18:31 -0700
Message-ID: <CABmPvSF7xLihcnk9bd3ZeK6Nr_DsQq2ypXV7wn8bU4UnQ0sKUg@mail.gmail.com>
Subject: Re: [PATCH v1 1/2] Bluetooth: btusb: Indicate Microsoft vendor
 extension for Intel 9460/9560 and 9160/9260
To:     Alain Michaud <alainmichaud@google.com>
Cc:     Marcel Holtmann <marcel@holtmann.org>,
        Joe Perches <joe@perches.com>,
        Bluetooth Kernel Mailing List 
        <linux-bluetooth@vger.kernel.org>,
        Luiz Augusto von Dentz <luiz.von.dentz@intel.com>,
        Alain Michaud <alainm@chromium.org>,
        "David S. Miller" <davem@davemloft.net>,
        Jakub Kicinski <kuba@kernel.org>,
        Johan Hedberg <johan.hedberg@gmail.com>,
        LKML <linux-kernel@vger.kernel.org>,
        netdev <netdev@vger.kernel.org>
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On Tue, Mar 24, 2020 at 12:32 PM Alain Michaud <alainmichaud@google.com> wrote:
>
> On Tue, Mar 24, 2020 at 2:35 PM Marcel Holtmann <marcel@holtmann.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.
Thanks for all your inputs. I will group these msft_vnd_ext_* into a
struct msft_vnd_ext with future refactoring in mind if new extensions
are introduced.