[PATCHv2] ASoC: omap-mcbsp: Do not attempt to change DAI sysclk if stream is active

[Jarkko Nikula <jhnikula@gmail.com>]

Attempt to change McBSP CLKS source while another stream is active is not
safe after commit d135865 ("OMAP: McBSP: implement functional clock
switching via clock framework") in 2.6.37.

CLKS parent clock switching using clock framework have to idle the McBSP
before switching and then activate it again. This short break can cause a
DMA transaction error to already running stream which halts and recovers
only by closing and restarting the stream.

This goes more fatal after commit e2fa61d ("OMAP3: l3: Introduce
l3-interconnect error handling driver") in 2.6.39 where l3 driver detects a
severe timeout error and does BUG_ON().

Fix this by not changing any configuration in omap_mcbsp_dai_set_dai_sysclk
if the McBSP is already active. This test should have been here just from
the beginning anyway.

Signed-off-by: Jarkko Nikula <jhnikula@gmail.com>
Cc: stable@kernel.org
---
v2:
- Returns -EBUSY from omap_mcbsp_dai_set_dai_sysclk if the input clock rate
  doesn't match with another stream's configuration and 0 otherwise.

For 2.6.37 and onward.

This issue is valid to those machine drivers that use the McBSP as a DAI link
master and are configuring the CLKS source (like sound/soc/omap/omap3pandora.c
in mainline).
---
 sound/soc/omap/omap-mcbsp.c |    6 ++++++
 1 files changed, 6 insertions(+), 0 deletions(-)

diff --git a/sound/soc/omap/omap-mcbsp.c b/sound/soc/omap/omap-mcbsp.c
index 07b7723..4b82290 100644
--- a/sound/soc/omap/omap-mcbsp.c
+++ b/sound/soc/omap/omap-mcbsp.c
@@ -516,6 +516,12 @@ static int omap_mcbsp_dai_set_dai_sysclk(struct snd_soc_dai *cpu_dai,
 	struct omap_mcbsp_reg_cfg *regs = &mcbsp_data->regs;
 	int err = 0;
 
+	if (mcbsp_data->active)
+		if (freq == mcbsp_data->in_freq)
+			return 0;
+		else
+			return -EBUSY;
+
 	/* The McBSP signal muxing functions are only available on McBSP1 */
 	if (clk_id == OMAP_MCBSP_CLKR_SRC_CLKR ||
 	    clk_id == OMAP_MCBSP_CLKR_SRC_CLKX ||
-- 
1.7.4.4