[alsa-devel] system suspend and live audio streams

[Jarkko Nikula]

On 04/16/2012 01:40 PM, Peter Ujfalusi wrote:
> Because we need to write registers (configure McPBSP).
> 
>> I don't know immediately does this require any major changes for McBSP
>> register access that are done in function calls before omap_mcbsp_start
>> (IRCC hwmod might set already ICLK gating for register access) but some
>> code is needed to deal with McBSP register cache restore (due OMAP
>> OFFMODE that might be hit) and most probably for McBSP FIFO draining as
>> well.
> 
I meant above if hwmod has already set ICLK so (was it autogating?) that
manual enable/disable cycle for ICLK may not be needed for register
access if clock is automatically gated. I have vague memory that I saw
something like this in hwmod for some block but I'm not sure about this.

But that reminds me that did we have some use-case where FCLK was needed
during register access?

> What we need to do is to have proper register store/restore for McBSP to
> support suspend during audio activity. But. Even with that if the McBSP
> is hitting OFF mode we will loose the McBSP FIFO content (invalidated).
> This means we are going to have missing samples. Probably the user will
> not going to notice it, but it is going to happen.

For register store/restore there is already much implemented thanks to
Janusz's register cache workaround for OMAP1510 :-)

For FIFO I was thinking, if possible, to drain it out before going to
suspend.

-- 
Jarkko