Re: can we disable/enable eSCO by using setsockopt of sco socket?

Hi Marcel,

2009/9/14 Marcel Holtmann [off-list ref]:

Hi,

quoted

When we connect a SCO socket, BlueZ decides whether to connect SCO or
eSCO type according to the remote feature. If the remote device
declares supporting eSCO in the remote feature, BlueZ will select eSCO
type to connect with it.

But in fact =A0there are some old carkits or headsets which are only
support SCO but wrongly declare to support eSCO, such as Motorola
HF850 and HS820 which use a very old CSR chip, so we have problem to
create sco connection with them.

We thought a method to resolve this issue, which is force to create
SCO type connection if we find the HFP version of one remote device is
less than 1.2. So we need a method to control the SCO type from user
space. We want to use setsockopt() functon to do that. The code change
in net/bluetooth/sco.c is like below,

@@ -653,12 +653,25 @@ static int sco_sock_setsockopt(struct socket *sock=

, int le

quoted

=A0{
=A0 =A0 =A0 =A0struct sock *sk =3D sock->sk;
=A0 =A0 =A0 =A0int err =3D 0;
+ =A0 =A0 =A0 u32 opt;

=A0 =A0 =A0 =A0BT_DBG("sk %p", sk);

=A0 =A0 =A0 =A0lock_sock(sk);

+ =A0 =A0 =A0 if (level !=3D SOL_SCO) {
+ =A0 =A0 =A0 =A0 =A0 =A0 =A0 err =3D -ENOPROTOOPT;
+ =A0 =A0 =A0 =A0 =A0 =A0 =A0 return err;
+ =A0 =A0 =A0 }
+
=A0 =A0 =A0 =A0switch (optname) {
+ =A0 =A0 =A0 case BT_DISABLE_ESCO:
+ =A0 =A0 =A0 =A0 =A0 =A0 =A0 if (get_user(opt, (u32 __user *) optval)) =

{

quoted

+ =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 err =3D -EFAULT;
+ =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 break;
+ =A0 =A0 =A0 =A0 =A0 =A0 =A0 }
+ =A0 =A0 =A0 =A0 =A0 =A0 =A0 disable_esco =3D opt;
+ =A0 =A0 =A0 =A0 =A0 =A0 =A0 break;
=A0 =A0 =A0 =A0default:
=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0err =3D -ENOPROTOOPT;
=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0break;


Then, in the user space, we can call setsockopt(fd, SOL_SCO,
BT_DISABLE_ESCO, &disabled, sizeof(disabled)) to force to connect SCO.

Do you agree with this change?

I don't. You first have to prove to me that this change is needed at
all. Show me the hcidump -X -V connections attempts for these carkits.

Also your analysis is wrong. BlueZ doesn't care if the remote headset
supports eSCO or not. We just care about if our local controller has the
synchronous setup commands. It is the job of the link manager inside the
controller firmware to either establish SCO or eSCO. And we do retry
with SCO if eSCO fails. This sounds more like the case that you have an
outdated kernel.

Regards

Marcel

Please excuse me for my inaccurate description. Actually it is LMP
layer to check the remote feature then decide which SCO type shall be
setup. So, if one remote device wrongly declare to support eSCO, it
will cause problem. I do know you have a retry mechanism to retry SCO
if eSCO failed, it is in below code in net/bluetooth/hci_event.c,
right?

	case 0x1c:	/* SCO interval rejected */
	case 0x1f:	/* Unspecified error */
		if (conn->out && conn->attempt < 2) {
			conn->pkt_type =3D (hdev->esco_type & SCO_ESCO_MASK) |
					(hdev->esco_type & EDR_ESCO_MASK);
			hci_setup_sync(conn, conn->link->handle);
			goto unlock;
		}
		/* fall through */

But the problem is, not all the returned error code can bring retry
SCO. So, we still got problem when connecting some devices because it
returns some error code else.

This is the hcidump log when we test SCO with HF850 carkit.

2009-09-03 17:26:29.093601 < HCI Command: Setup Synchronous Connection (0x0=
1|0x0
028) plen 17
    handle 1 voice setting 0x0060
2009-09-03 17:26:29.094608 > HCI Event: Command Status (0x0f) plen 4
    Setup Synchronous Connection (0x01|0x0028) status 0x00 ncmd 1
2009-09-03 17:26:34.190952 > HCI Event: Synchronous Connect Complete (0x2c)=
 plen
 17
    status 0x10 handle 257 bdaddr 00:50:CD:20:BA:E6 type eSCO
    Error: Connection Accept Timeout Exceeded
2009-09-03 17:26:34.191196 < HCI Command: Setup Synchronous Connection (0x0=
1|0x0
028) plen 17
    handle 1 voice setting 0x0060

From the log you can see, the eSCO connection failed in 5 seconds with

the error "0x10 Timeout Exceeded", and it do not retry SCO again.

In order to resolve such issue, we have thought about two methods to
resolve this.

The first one is, add a new case for "0x10" error code and then retry
SCO. We do have tested this, SCO can be setup, but the 5 seconds delay
can not be eliminated.

The second one is, we hope to force to use the sco type of SCO for
some special devices which have compatible issue with eSCO. We can
force to connect SCO by calling hci_add_sco() or hci_setup_sync() with
limited pkt_type for those kind of devices. This is why we want to add
a DISABLE_ESCO option into setsockopt() function.


Thank you,
Zhu Lan