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

[NeilBrown <neilb@suse.de>]

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On Fri, 3 Feb 2012 19:06:19 -0700 (MST) Paul Walmsley <paul@pwsan.com> wrote:

> Hi Neil
> 
> On Sat, 4 Feb 2012, NeilBrown wrote:
> 
> > 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


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