minor device number...

I am taking a standar d version of a custom serial driver and making a
streams driver from it. The problem I have is that the current driver
uses device minor number as an index to the correct port in the FPGA.
How can I get the device minor number in the driver.  I know how to get
it from the open(), but I need it for the read and write streams that
only have mblk_t and queue_t to work from.

Any suggestions??

Bill