On Mon, Jun 9, 2014 at 4:18 PM, Rob Herring [off-list ref] wrote:

It should do auto detect of the baud-rate if it is not specified which
for 8250 is just reading the baud-rate divider and calculating the
baud-rate using the uart clock. It should just reprogram the divider
with the same divider value. I don't see anything obvious why this
would have broken.

Something very weird is happening.  Output is good so long as I put the
trailing ",115200" on the command line.

But I made early_serial8250_setup() printk() the return value it got
from probe_baud() - in case is was somehow getting 115201 or some
other silly value ... nope. Exactly 115200.

I also can't explain why the "noise" comes and goes a dozen
times during boot,

Does some other place in the kernel look at the "uart..." command
line argument?

-Tony