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Subject: Re: [PATCH RFC] bluetooth: add support for some old headsets
From:   Marcel Holtmann <marcel@holtmann.org>
In-Reply-To: <6f271bf7-04ee-c971-9c69-de3f696769ed@omprussia.ru>
Date:   Tue, 28 Jul 2020 09:16:59 +0200
Cc:     Johan Hedberg <johan.hedberg@gmail.com>,
        Bluetooth Kernel Mailing List 
        <linux-bluetooth@vger.kernel.org>,
        "David S. Miller" <davem@davemloft.net>,
        Jakub Kicinski <kuba@kernel.org>, netdev@vger.kernel.org,
        Ildar Kamaletdinov <i.kamaletdinov@omprussia.ru>
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To:     Sergey Shtylyov <s.shtylyov@omprussia.ru>
Sender: linux-bluetooth-owner@vger.kernel.org
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Hi Sergey,

>>>>>> The MediaTek Bluetooth platform (MT6630 etc.) has a peculiar implementation
>>>>>> for the eSCO/SCO connection via BT/EDR: the host controller returns error
>>>>>> code 0x20 (LMP feature not supported) for HCI_Setup_Synchronous_Connection
>>>>>> (0x0028) command without actually trying to setup connection with a remote
>>>>>> device in case such device (like Digma BT-14 headset) didn't advertise its
>>>>>> supported features.  Even though this doesn't break compatibility with the
>>>>>> Bluetooth standard it breaks the compatibility with the Hands-Free Profile
>>>>>> (HFP).
>>>>>> 
>>>>>> This patch returns the compatibility with the HFP profile and actually
>>>>>> tries to check all available connection parameters despite of the specific
>>>>>> MediaTek implementation. Without it one was unable to establish eSCO/SCO
>>>>>> connection with some headsets.
> [...]
>>>>>> Signed-off-by: Sergey Shtylyov <s.shtylyov@omprussia.ru>
>>>>>> 
>>>>>> ---
>>>>>> This patch is against the 'bluetooth-next.git' repo.
>>>>>> 
>>>>>> net/bluetooth/hci_event.c |    8 ++++++++
>>>>>> 1 file changed, 8 insertions(+)
>>>>>> 
>>>>>> Index: bluetooth-next/net/bluetooth/hci_event.c
>>>>>> ===================================================================
>>>>>> --- bluetooth-next.orig/net/bluetooth/hci_event.c
>>>>>> +++ bluetooth-next/net/bluetooth/hci_event.c
>>>>>> @@ -2187,6 +2187,13 @@ static void hci_cs_setup_sync_conn(struc
>>>>>> 	if (acl) {
>>>>>> 		sco = acl->link;
>>>>>> 		if (sco) {
>>>>>> +			if (status == 0x20 && /* Unsupported LMP Parameter value */
>>>>>> +			    sco->out) {
>> 
>>    Actually, I was expecting that you'd tell me to create a HCI quirk for this situation.
>> I have a patch doing that but I haven't been able to locate the driver in which to set this
>> quirk flag...
> 
>   And that's no wonder! The BT driver that needs this patch is out-of-tree (and not even open
> source, it seems) as we have finally ascertained with Ildar... Is there any interest in the
> "preparatory" patch that lowers the indentation levels in hci_cs_setup_sync_conn()?

how is it possible that there is an out-of-tree Bluetooth driver. Seems odd. Maybe want to submit that upstream first.

Regards

Marcel