From: NeilBrown [mailto:neilb@suse.de]
Sent: Monday, February 06, 2012 5:58 PM
To: Woodruff, Richard

Apologies for mangled mails... I am years over due ditching current method.

I don't think it is really OK to drop chars on the UART-to-Debug console.
However it is OK to drop the BAUD rate to 57600 where we can wake up in
time
for to catch the first bit.  So if you want power saving, drop the console
buad rate.

So I would suggest:
 - remove the autosuspend timeouts
 - allow runtime_pm to shutdown the device when it is not open, or when
   rate is 57600 or below, or when 'CREAD' is clear
 - keep runtime_pm active whenever there are bytes in the output queue or
   fifo

Yes slower baud + use of flow control should help. OMAP4 is like 10x better than OMAP2 with OMAP3 in middle.

The only case that wouldn't support is when a device will wake up the SOC
by
sending a non-break character which it is OK to receive corrupted.  The
tty
would have to be in !CREAD for that to happen, and then there would be no
way
for the app to know that a non-break character was received.
Would it be reasonable to treat any input while CREAD is clear as a break?

Others would have to comment on this.  I never took this step as I was ok with degradation on debug console.

If ever I wanted better logs I tended to telnet/ssh in on a network port which was better at retry at higher level.

Regards,
Richard W.