If the machine driver doesn't call snd_soc_dai_set_sysclk() the
SCLK is assumed to be sample_rate * sample_bits * 2 (that is, the
rate necessary for a standard I2S frame).
But 24-bit samples can be sent in either a 24-bit slot or a 32-bit
slot. If the PLL is configured for a 24-bit slot, but a 32-bit slot is
used, cs42l42 will be overclocked.
Ultimately it is the machine driver's responsibilty to call
snd_soc_dai_set_sysclk() if SLK will be different from the standard
I2S rate. However, it is convenient to assume 32-bit slots to allow
this common case without needing special machine driver support. The
machine driver then only has to set SCLK if the slots are 24-bit, but
if it fails to do this cs42l42 won't be overclocked.
Signed-off-by: Richard Fitzgerald <rf@xxxxxxxxxxxxxxxxxxxxx>
---
sound/soc/codecs/cs42l42.c | 7 +++++++
1 file changed, 7 insertions(+)
diff --git a/sound/soc/codecs/cs42l42.c b/sound/soc/codecs/cs42l42.c
index b2ee51443a22..3677ed4670d0 100644
--- a/sound/soc/codecs/cs42l42.c
+++ b/sound/soc/codecs/cs42l42.c
@@ -844,6 +844,13 @@ static int cs42l42_pcm_hw_params(struct snd_pcm_substream *substream,
if (channels == 1)
cs42l42->bclk *= 2;
+ /*
+ * Assume 24-bit samples are in 32-bit slots, to prevent SCLK being
+ * more than assumed (which would result in overclocking).
+ */
+ if (params_width(params) == 24)
+ cs42l42->bclk = (cs42l42->bclk / 3) * 4;
+
switch(substream->stream) {
case SNDRV_PCM_STREAM_CAPTURE:
if (channels == 2) {
--
2.11.0
