[alsa-devel] [PATCH] OMAP: McBSP: Do not use extensive spin locks for dma_op_mode

Peter Ujfalusi peter.ujfalusi at nokia.com
Wed Oct 28 06:52:23 CET 2009

On Tuesday 27 October 2009 16:00:00 ext Jarkko Nikula wrote:
> On Tue, 27 Oct 2009 13:07:23 +0200
> Eero Nurkkala <ext-eero.nurkkala at nokia.com> wrote:
> > Otherwise, that spinlocking is highly unnecessary and things are
> > far better without than with it. The only case it could be useful
> > is in SMPs, but OMAPs are not such quite yet - and when they
> > are, things will need to be re-though anyway.
> Following commit is suggesting that mcbsp code *must* be SMP safe
> already now:
> commit a5b92cc348299c20be215b9f4b50853ecfbf3864
> Author: Syed Rafiuddin <rafiuddin.syed at ti.com>
> Date:   Tue Jul 28 18:57:10 2009 +0530
>     ARM: OMAP4: Add McBSP support

Yeah, but I think this locking issue has nothing to do with SMP safe or not.
On playback start in omap_mcbsp_request the mcbsp->free is cleared.
Further modification to the dma_op_mode in dma_op_mode_store is not allowed if 
the mcbsp port is in use, thus the dma_op_mode is protected against change while 
the port is in use (ensuring that the mode is same in omap34xx_mcbsp_request and 
omap_mcbsp_get_dma_op_mode functions). This alone makes the use of spinlock 
around the dma_op_mode unnecessary.


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