[alsa-devel] [PATCH] ASoC: OMAP: mcbsp: ensure that CLKX and CLKR are not used as ouput pins when they are used as input clock for the SRG.

[Thomas Niederprüm]

Am Freitag, den 16.01.2015, 11:15 +0200 schrieb Peter Ujfalusi:
> On 01/16/2015 12:28 AM, Thomas Niederprüm wrote:
> > This patch fixes faulty behaviour in a setup where the input clock for
> > the SRG is fed through the CLKR pin but the McBSP is configured to be
> > master (SND_SOC_DAIFMT_CBS_CFS). In that case of course CLKR must not be
> > configured as output pin. Otherwise the input clock is messed up
> > horribly. The same reasoning applies if CLKX is configured as input for
> > the SRG.
> 
> If CLKX/CLKR is used as input clock for McBSP then the CBS_CFS is not valid.
> In this case you need to use CBM_CFS.
> 
The setup I am using is the following: McBSP is driving an external i2s
DAC as master by supplying CLKX and FSX and DX. The DAC only supports
i2s slave mode. For synchronization the DAC and the McBSP should share
the same master/reference clock (CLKM). Since I don't need the receive
path of the McBSP anyway for the DAC I can use the CLKR pin to insert
the CLKM as input to the SRG. I think in this scenario CBS_CFS is valid
since the McBSP acts as master (for the transmit path)

It might be more common to use the CKLS pin to inject the reference
clock, but the beagleboard-xm I am using already hard wired this to the
built-in twl4030 codec which makes it unusable.

> > 
> > Signed-off-by: Thomas Niederprüm <niederp at physik.uni-kl.de>
> > ---
> >  sound/soc/omap/omap-mcbsp.c | 4 ++++
> >  1 file changed, 4 insertions(+)
> > 
> > diff --git a/sound/soc/omap/omap-mcbsp.c b/sound/soc/omap/omap-mcbsp.c
> > index bd3ef2a..c89f562 100644
> > --- a/sound/soc/omap/omap-mcbsp.c
> > +++ b/sound/soc/omap/omap-mcbsp.c
> > @@ -530,8 +530,12 @@ static int omap_mcbsp_dai_set_dai_sysclk(struct snd_soc_dai *cpu_dai,
> >  
> >  	case OMAP_MCBSP_SYSCLK_CLKX_EXT:
> >  		regs->srgr2	|= CLKSM;
> > +		regs->pcr0	|= SCLKME;
> > +		regs->pcr0	&= ~CLKXM;
> > +		break;
> >  	case OMAP_MCBSP_SYSCLK_CLKR_EXT:
> >  		regs->pcr0	|= SCLKME;
> > +		regs->pcr0	&= ~CLKRM;
> >  		break;
> >  	default:
> >  		err = -ENODEV;
> > 
> 
> 

-- 
Thomas Niederprüm
TU Kaiserslautern
FB Physik (AG Ott)
Erwin-Schrödinger-Str. 46/431
67663 Kaiserslautern
Tel.: 0631 205 2387
Fax: 0631 205 3906