Re: Serial core problems on embedded PPC

On Mon, Jul 29, 2002 at 10:00:10AM +0100, Russell King wrote:

On Mon, Jul 29, 2002 at 02:08:24PM +1000, David Gibson wrote:

quoted

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.

It's vital that you mention the kernel version you're using; some of
these problems sound like 2.5.28.

Sorry.  I'm working off the linuxppc-2.5 BK tree, which is currently
at 2.5.29.

quoted

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.

There is no easy solution for this.  Alan said we must not drop support
for serial console initialisation early on in the kernel setup, which
means before the memory subsystems are initialised.

quoted

I added support for these into 8250.c, but ran into further troubles.

I suspect a 2.5.28 kernel; please confirm and we'll that it from there.

2.5.29 based BK, actually.

quoted

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.

I don't see there being an easy way to kill this off:

1. serial_struct is a userspace API.

Ok.

2. old_serial_port glues asm/serial.h into 8250.c; asm/serial.h can't be
   changed because (mainly) ppc uses it elsewhere.  Other architectures
   seem to do the same sort of thing.

I think PPC's use of asm/serial.h in the bootloader needs to go away
anyway.  Could old_serial_port at least change base_baud to baud_base
to match serial_struct and serial_state.  That way a designated
initializer will work in either context.

Unless ppc and others are willing to put up with major breakage when I
change asm/serial.h, I don't see this getting cleaned up.  Comments on
this area welcome.

Well, the machines I'm working on are totally broken now, so...

--
David Gibson			| For every complex problem there is a
david@gibson.dropbear.id.au	| solution which is simple, neat and
				| wrong.
http://www.ozlabs.org/people/dgibson

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