[alsa-devel] [PATCH 06/20] OMAP: McBSP: Use appropriate value for startup delay

ext-Eero.Nurkkala at nokia.com ext-Eero.Nurkkala at nokia.com
Fri Jul 31 09:21:30 CEST 2009

Jarkko Nikula [jhnikula at gmail.com] wrote:
> Are you sure this change is necessary? CLKSRG is kind of master clock
> to McBSP so original stetson guessed (?) 100 us should be fine for all
> serial links where bit clock is higher than 20 kHz.

The McBSP / DMA stuff doesn't really work properly, when PM is enabled
to full extent. The first DMA goes in _before_ the omap_mcbsp_start(),
so the higher delay compensates DMA misbehavior in a way...

.. L/R channels also may switch at random initially with full PM enabled.
So the L/R fix is only working, if no PM is enabled (sigh).

Need to make that work fine (no L/R switching and early no DMA completions)
to get rid of the higher, 500us, timeout. Maybe try not having 
XCCR/RCCR dma enable bit initially, but enabling them at omap_mcbsp_start()?
(I'd try if I wasn't also on vacation).

- Eero--
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