Serial core problems on embedded PPC

David Gibson david at
Mon Jul 29 14:08:24 EST 2002

I've been trying to get the new serial core stuff working on a PPC 4xx
machine (an EP405 board, specifically).  This is proving more
difficult than I expected.

In 8250.c, it appears that in order for a port to be used for the
serial console it must be defined "old style" with SERIAL_PORT_DFNS,
rather than being registered with register_serial() (because
serial8250_console_setup() indexs into the serial8250_ports array)).
This presents a small problem for 4xx, since it's serial ports are
memory mapped and the new old_serial_port structure can't represent
these.  I added support for these into 8250.c, but ran into further

The kernel now gets into an infinite loop when trying to open
/dev/console in init().  The loop is occuring in tty_open() - the open
fails and it loops back to the retry_open: label.  This seems to be
happening because the uart_port structure is ending up with the type
field set to PORT_UNKNOWN.  However, I'm getting confused attempting
to work out where this field ought to be set, and why it isn't.

The current plethora of similar-but-not-the-same structures describing
serial ports (serial_state, serial_struct, uart_port, old_serial_port)
is also rather confusing.  I'm guessing some of these are deprecated
and remain only as an aid to transition, but I'm not sure which.

David Gibson			| For every complex problem there is a
david at	| solution which is simple, neat and
				| wrong.

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