Re: [rfc]btusb with SCO support

[Marcel Holtmann <marcel@holtmann.org>]

Hi Alan,

> > example have the USB core queue submitted URBs until the new alternate
> > setting has been selected?
> 
> this one's for you. Is there a deeper reason we enable and disable endpoints
> therein?

just let me give you details on rational behind my question. A Bluetooth
USB device uses two interfaces. The first one for control (commands),
interrupt (event) and bulk (ACL data) endpoints. The second interface
contains the isoc (SCO data) endpoints.

T:  Bus=02 Lev=01 Prnt=01 Port=00 Cnt=01 Dev#=  2 Spd=12  MxCh= 0
D:  Ver= 2.00 Cls=e0(unk. ) Sub=01 Prot=01 MxPS=64 #Cfgs=  1
P:  Vendor=0bf8 ProdID=1003 Rev=53.42
C:* #Ifs= 3 Cfg#= 1 Atr=c0 MxPwr=  0mA
I:* If#= 0 Alt= 0 #EPs= 3 Cls=e0(unk. ) Sub=01 Prot=01 Driver=btusb
E:  Ad=81(I) Atr=03(Int.) MxPS=  16 Ivl=1ms
E:  Ad=02(O) Atr=02(Bulk) MxPS=  64 Ivl=0ms
E:  Ad=82(I) Atr=02(Bulk) MxPS=  64 Ivl=0ms
I:* If#= 1 Alt= 0 #EPs= 2 Cls=e0(unk. ) Sub=01 Prot=01 Driver=btusb
E:  Ad=03(O) Atr=01(Isoc) MxPS=   0 Ivl=1ms
E:  Ad=83(I) Atr=01(Isoc) MxPS=   0 Ivl=1ms
I:  If#= 1 Alt= 1 #EPs= 2 Cls=e0(unk. ) Sub=01 Prot=01 Driver=btusb
E:  Ad=03(O) Atr=01(Isoc) MxPS=   9 Ivl=1ms
E:  Ad=83(I) Atr=01(Isoc) MxPS=   9 Ivl=1ms
I:  If#= 1 Alt= 2 #EPs= 2 Cls=e0(unk. ) Sub=01 Prot=01 Driver=btusb
E:  Ad=03(O) Atr=01(Isoc) MxPS=  17 Ivl=1ms
E:  Ad=83(I) Atr=01(Isoc) MxPS=  17 Ivl=1ms
I:  If#= 1 Alt= 3 #EPs= 2 Cls=e0(unk. ) Sub=01 Prot=01 Driver=btusb
E:  Ad=03(O) Atr=01(Isoc) MxPS=  25 Ivl=1ms
E:  Ad=83(I) Atr=01(Isoc) MxPS=  25 Ivl=1ms
I:  If#= 1 Alt= 4 #EPs= 2 Cls=e0(unk. ) Sub=01 Prot=01 Driver=btusb
E:  Ad=03(O) Atr=01(Isoc) MxPS=  33 Ivl=1ms
E:  Ad=83(I) Atr=01(Isoc) MxPS=  33 Ivl=1ms
I:  If#= 1 Alt= 5 #EPs= 2 Cls=e0(unk. ) Sub=01 Prot=01 Driver=btusb
E:  Ad=03(O) Atr=01(Isoc) MxPS=  49 Ivl=1ms
E:  Ad=83(I) Atr=01(Isoc) MxPS=  49 Ivl=1ms
I:* If#= 2 Alt= 0 #EPs= 0 Cls=fe(app. ) Sub=01 Prot=00 Driver=(none)

The second interface contains 6 alternate settings and you have to
select them based on your voice setting (8-bit or 16-bit) and the number
of SCO connections (0-3).

The Bluetooth specification has the details, but when using 16-bit input
data and one SCO connection, you have to select alternate setting #2. If
no SCO connections are open, we have to go with setting #0.

T:  Bus=02 Lev=01 Prnt=01 Port=00 Cnt=01 Dev#=  2 Spd=12  MxCh= 0
D:  Ver= 2.00 Cls=e0(unk. ) Sub=01 Prot=01 MxPS=64 #Cfgs=  1
P:  Vendor=0bf8 ProdID=1003 Rev=53.42
C:* #Ifs= 3 Cfg#= 1 Atr=c0 MxPwr=  0mA
I:* If#= 0 Alt= 0 #EPs= 3 Cls=e0(unk. ) Sub=01 Prot=01 Driver=btusb
E:  Ad=81(I) Atr=03(Int.) MxPS=  16 Ivl=1ms
E:  Ad=02(O) Atr=02(Bulk) MxPS=  64 Ivl=0ms
E:  Ad=82(I) Atr=02(Bulk) MxPS=  64 Ivl=0ms
I:  If#= 1 Alt= 0 #EPs= 2 Cls=e0(unk. ) Sub=01 Prot=01 Driver=btusb
E:  Ad=03(O) Atr=01(Isoc) MxPS=   0 Ivl=1ms
E:  Ad=83(I) Atr=01(Isoc) MxPS=   0 Ivl=1ms
I:  If#= 1 Alt= 1 #EPs= 2 Cls=e0(unk. ) Sub=01 Prot=01 Driver=btusb
E:  Ad=03(O) Atr=01(Isoc) MxPS=   9 Ivl=1ms
E:  Ad=83(I) Atr=01(Isoc) MxPS=   9 Ivl=1ms
I:* If#= 1 Alt= 2 #EPs= 2 Cls=e0(unk. ) Sub=01 Prot=01 Driver=btusb
E:  Ad=03(O) Atr=01(Isoc) MxPS=  17 Ivl=1ms
E:  Ad=83(I) Atr=01(Isoc) MxPS=  17 Ivl=1ms
I:  If#= 1 Alt= 3 #EPs= 2 Cls=e0(unk. ) Sub=01 Prot=01 Driver=btusb
E:  Ad=03(O) Atr=01(Isoc) MxPS=  25 Ivl=1ms
E:  Ad=83(I) Atr=01(Isoc) MxPS=  25 Ivl=1ms
I:  If#= 1 Alt= 4 #EPs= 2 Cls=e0(unk. ) Sub=01 Prot=01 Driver=btusb
E:  Ad=03(O) Atr=01(Isoc) MxPS=  33 Ivl=1ms
E:  Ad=83(I) Atr=01(Isoc) MxPS=  33 Ivl=1ms
I:  If#= 1 Alt= 5 #EPs= 2 Cls=e0(unk. ) Sub=01 Prot=01 Driver=btusb
E:  Ad=03(O) Atr=01(Isoc) MxPS=  49 Ivl=1ms
E:  Ad=83(I) Atr=01(Isoc) MxPS=  49 Ivl=1ms
I:* If#= 2 Alt= 0 #EPs= 0 Cls=fe(app. ) Sub=01 Prot=00 Driver=(none)

So we can't have isoc URBs running all them time since that would drain
power. The old hci_usb did it this way and was an obvious issue showing
up on powertop.

The Bluetooth subsystem calls our notify() callback when the number of
connection or the voice setting changes. However this context can't
sleep and thus we can't call usb_set_interface(). Right now are using a
workqueue, but that is not an optimal solution since as Oliver pointed
correctly out, we have no idea when this gets scheduled.

My question is if we can have a usb_set_interface() version that we can
call from interrupt context and that will queue the URBs that we submit
in between until the new alternate setting has been selected.

I personally think the Bluetooth USB specification is broken and a bad
design, but that is what we have at the moment.

Regards

Marcel