hciattach timeout - blocks at read() call

Hi,
I am currently trying to get bluetooth working, but hciattach always gives me initialization timeout.
I have a W2CBW003 module which has a marvel wlan module and a CSR BC04 bt module.
I call hciattach like this:
hciattach ttyS1 csr

The LED is flashing a few times but nothing else happens.

I added some debug printf's to the csr() initialize function and the read_hci_event() in hciattach.c and it turned out that read_hci_event blocks on the read() call on line 164.

My question: is this a known issue? or someone knows what the problem could be ?

thanks & greetings
hannes