BDW boards using this machine driver supports only stereo capture and
playback. Implement a constraint to enforce it.

Signed-off-by: Brent Lu <brent...@intel.com>
---
 sound/soc/intel/boards/bdw-rt5677.c | 33 +++++++++++++++++++++++++++++++++
 1 file changed, 33 insertions(+)

diff --git a/sound/soc/intel/boards/bdw-rt5677.c 
b/sound/soc/intel/boards/bdw-rt5677.c
index 4a4d335..a312b55 100644
--- a/sound/soc/intel/boards/bdw-rt5677.c
+++ b/sound/soc/intel/boards/bdw-rt5677.c
@@ -22,6 +22,8 @@
 
 #include "../../codecs/rt5677.h"
 
+#define DUAL_CHANNEL 2
+
 struct bdw_rt5677_priv {
        struct gpio_desc *gpio_hp_en;
        struct snd_soc_component *component;
@@ -245,6 +247,36 @@ static int bdw_rt5677_init(struct snd_soc_pcm_runtime *rtd)
        return 0;
 }
 
+static const unsigned int channels[] = {
+       DUAL_CHANNEL,
+};
+
+static const struct snd_pcm_hw_constraint_list constraints_channels = {
+       .count = ARRAY_SIZE(channels),
+       .list = channels,
+       .mask = 0,
+};
+
+static int bdw_fe_startup(struct snd_pcm_substream *substream)
+{
+       struct snd_pcm_runtime *runtime = substream->runtime;
+
+       /*
+        * On this platform for PCM device we support,
+        * stereo
+        */
+
+       runtime->hw.channels_max = DUAL_CHANNEL;
+       snd_pcm_hw_constraint_list(runtime, 0, SNDRV_PCM_HW_PARAM_CHANNELS,
+                                          &constraints_channels);
+
+       return 0;
+}
+
+static const struct snd_soc_ops bdw_rt5677_fe_ops = {
+       .startup = bdw_fe_startup,
+};
+
 /* broadwell digital audio interface glue - connects codec <--> CPU */
 SND_SOC_DAILINK_DEF(dummy,
        DAILINK_COMP_ARRAY(COMP_DUMMY()));
@@ -273,6 +305,7 @@ static struct snd_soc_dai_link bdw_rt5677_dais[] = {
                },
                .dpcm_capture = 1,
                .dpcm_playback = 1,
+               .ops = &bdw_rt5677_fe_ops,
                SND_SOC_DAILINK_REG(fe, dummy, platform),
        },
 
-- 
2.7.4

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