Re: [PATCH 06/20] OMAP: McBSP: Use appropriate value for startup delay

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



On Fri, 31 Jul 2009 09:21:30 +0200
<ext-Eero.Nurkkala@xxxxxxxxx> wrote:

> Jarkko Nikula [jhnikula@xxxxxxxxx] 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).
> 
Ok, 500 us is not so long delay here compared to benefits but it would
be good to have a little revisit comment for future reference. I think
that by default 100 us provides enough time for two CLKSRG cycles but
due some unknown PM related, clock gating etc. reason it must be
extended to 500 us now.

-- 
Jarkko
--
To unsubscribe from this list: send the line "unsubscribe linux-omap" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html

[Index of Archives]     [Linux Arm (vger)]     [ARM Kernel]     [ARM MSM]     [Linux Tegra]     [Linux WPAN Networking]     [Linux Wireless Networking]     [Maemo Users]     [Linux USB Devel]     [Video for Linux]     [Linux Audio Users]     [Yosemite Trails]     [Linux Kernel]     [Linux SCSI]

  Powered by Linux