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

[Paul Walmsley]

On Sat, 4 Feb 2012, Woodruff, Richard wrote:

> When you have aggressive PM working at the SOC level you many times lost 
> a character on UART every since OMAP2. A strange but true statement is 
> it is nice to see it losing a character on mainline as it as in 
> indication that PM is likely working.

We've been losing wakeup characters in mainline for many years now ;-)

> One irritation was some internal interrupt sources were not linked to 
> low power wakeup events. If you were in interrupt mode and got 
> characters below watermark you could sleep before interrupt status 
> showed up (as you had to wait several frame times before functional 
> interrupt asserted) but there was no wake at anticipated frame timeout 
> because lack of linking of internal event to wake event.

Indeed, it seems that we are just now working around these wakeup-related 
bugs.  Kind of surprising that no errata showed up for them.

What's particularly remarkable is that it looks like the UARTs will 
idle-ack while their transmit FIFOs have data in them (!)


- Paul