[alsa-devel] [PATCH v2] 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]

This patch fixes faulty behaviour in a setup where the input clock for the
SRG is fed through the CLKR/CLKX pin but the McBSP is configured to be
master (SND_SOC_DAIFMT_CBS_CFS). In that case of course CLKR/CLKX must
not be configured as output pin. Otherwise the input clock is messed up
horribly.

This patch makes it possible to use the CLKR/CLKX pin rather than CLKS to
inject a reference clock in setups where McBSP is master and not both
rx and tx are used. However for this to work it has to be ensured that
set_dai_sysclk() is called after set_dai_fmt().

This was tested on a beagleboard-xm using McBSP1 to drive a i2s DAC through
the tx lines (CLKX,FSX,DX). Using this patch the CLKR pin is used to inject
an external reference clock.

changes since v1:
- added comments explaining the bit masking to disable output on CLKR/CLKX

Signed-off-by: Thomas Niederprüm <niederp at physik.uni-kl.de>
---
 sound/soc/omap/omap-mcbsp.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/sound/soc/omap/omap-mcbsp.c b/sound/soc/omap/omap-mcbsp.c
index bd3ef2a..c37f606 100644
--- a/sound/soc/omap/omap-mcbsp.c
+++ b/sound/soc/omap/omap-mcbsp.c
@@ -530,8 +530,19 @@ 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;
+		/*
+		 * If McBSP is master but yet the CLKX/CLKR pin drives the SRG,
+		 * disable output on those pins. This enables to inject the 
+		 * reference clock through CLKX/CLKR. For this to work 
+		 * set_dai_sysclk() _needs_ to be called after set_dai_fmt().
+		 */
+		regs->pcr0	&= ~CLKXM;
+		break;
 	case OMAP_MCBSP_SYSCLK_CLKR_EXT:
 		regs->pcr0	|= SCLKME;
+		/* Disable ouput on CLKR pin in master mode */
+		regs->pcr0	&= ~CLKRM;
 		break;
 	default:
 		err = -ENODEV;
-- 
2.1.1