patch "tty: serial: OMAP: ensure FIFO levels are set correctly in non-DMA" added to tty tree

[Woodruff, Richard]

> From: NeilBrown [mailto:neilb at 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.