Re: [Bluez-devel] HCI USB driver and SCO support

[Marcel Holtmann <marcel@rvs.uni-bielefeld.de>]

Hi James,

> > but without choosing the correct ISOC alternate setting it is useless :(
> 
> I think the "ISOC alternate setting" are USB specific, so I think work 
> should be contained in hci_usb, and not require core modifications.

you basicly have two options

	1) Parse events and commands inside the driver
	2) Let the core send a notify event to the driver

I already have done 1) for the number of SCO connections. It is very
easy and it didn't blow-up the hci_usb code very much. After getting
dynamic starting and stoping of ISOC URB's working I realized that all
this won't help, if we don't adjust the ISOC alternate setting on
demand. As I already said, the ISOC alternate setting depends on the
number of SCO connections and the current voice setting (8 or 16 bit).
So I have to parse the read_voice_setting and write_voice_setting
commands and results. If you try this by yourself you will see, that
this is not a job, which should be done in the driver. Keep the driver
quite stupid and let it be what it is meant to be - a host transport
driver.

And after knowing all this, the only way that makes sense at the moment
is 2). Look at my patch and you will see that it is a clean extension to
the core, because it only notify the driver about special events. What
to do with this information is up to the driver.

> To this end, I think it would be helpful to separate INT and BULK 
> traffic from SCO traffic.
> SCO is realtime, INT and BULK are not, so they require different buffer 
> handling.
> To this end, INT and BULK work well with queues, and SCO are better 
> suited to ring buffers.

This is not quite correct. The hci_usb driver and the HCI core have to
handle SCO traffic, but they don't have to know much about it. It is a
packet type which have to be send and received. Nothing more, nothing
less. The hci_usb driver uses ISOC endpoints to transfer SCO packets and
BULK endpoints to transfer ACL packets. All other buffering which is
needing have to be done in the sco module.

May I have to repeat myself - let us first finish the hci_usb driver
with full SCO support. Max has agreed on my core change and I will push
it for 2.4 and 2.5/2.6, so the hci_usb driver can be fixed very easy.

Regards

Marcel




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