[Xen-devel] [patch] auto serial port configuration

[Hollis Blanchard <hollisb@xxxxxxxxxx>]

This patch allows runtime autoconfiguration of the serial console.

Right now on PowerPC, we're configuring the serial port by appending 
"com1=..." to cmdline, which is inflexible and inefficient.

Also, we're using a couple systems whose firmware use different baud rates for 
the serial console (115200 and 19200). It is annoying or impossible to set 
environment variables in these firmwares right now, which makes 
autoconfiguration important.

This patch does a few things:
- It allows us to automatically enable the serial console ("console=com1").
- It gives the ns16550 parameters reasonable defaults (8n1).
- If baud is unspecified, do not reconfigure the ns16550 baud rate (use 
whatever firmware was using).
- It allows us to automatically configure ns16550 parameters 
("com1=baud,..."). All parameters are optional (so you can selectively 
override the defaults).

I've included the PowerPC code so you could see an example of a user. (Side 
note: Open Firmware systems provide the system's hardware configuration in a 
data structure called the "device tree". In particular, the ISA IO base, used 
to emulate ISA IO on systems that only have MMIO, is at an arbitrary physical 
address; we only know where that is at runtime, when the device tree tells 
us.)

If there are no objections, please apply.

Signed-off-by: Hollis Blanchard <hollisb@xxxxxxxxxx>

-- 
Hollis Blanchard
IBM Linux Technology Center

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