On Fri, 3 Feb 2012 19:06:19 -0700 (MST) Paul Walmsley [off-list ref] wrote:

Hi Neil

On Sat, 4 Feb 2012, NeilBrown wrote:

quoted

Guess what happens if I set autosuspend_delay_ms to 0?
Massive transmit problems.  Driver can hardly get anything out before the
UART's fclk is cut...

Just reproduced this on 35xx BeagleBoard.  Looks like the UART is indeed 
going idle while the TX FIFO has bytes in it.

That makes me happy :-)

Here's a patch that helps.  It seems to work down to an 
autosuspend_delay_ms of 1 ms.  Without it, the best I can get is 8 ms.

Of course, ideally it should work fine at autosuspend_delay_ms = 0, so 
likely there's some other infelicity that we're currently missing.

Neil, care to give this a test and confirm it on your setup?

Yes, that seems to make the output corruption go away.

Even with small autosuspend_delay_ms down to 0 it doesn't corrupt output,
but as the first input byte is corrupted, I cannot really type with those
setting (so I ssh to gain control again).

The patch disables the IDLEMODE_SMART setting that happens on runtime
suspend/resume so that the IDLEMODE_NO setting stays in force.

So it clearly isn't "stopping the clocks" that is the problem - as I first
imagined - but rather the SIDLE handshake isn't doing what we think it should
do.

Thanks,
NeilBrown