ASoC: mxs-saif: Fix channel swap for 24-bit format

Playing 24-bit format file leads to channel swap on mx28 and the reason is that
the current driver performs one write/read to/from the SAIF_DATA register to
trigger the transfer.

This approach works fine for S16_LE case because SAIF_DATA is a 32-bit register
and thus is capable of storing the 16-bit left and right channels, but for the
S24_LE case it can only store one channel, so in order to not lose the FIFO sync
an extra read/write is needed.

Reported-by: Dan Winner <DWinner@tc-helicon.com>
Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>
Tested-by: Dan Winner <DWinner@tc-helicon.com>
Acked-by: Dong Aisheng <dong.aisheng@linaro.org>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>

1 files changed, 12 insertions, 4 deletions

diff --git a/sound/soc/mxs/mxs-saif.c b/sound/soc/mxs/mxs-saif.c
index 93380cc7cf97..c294fbb523fc 100644
--- a/sound/soc/mxs/mxs-saif.c
+++ b/sound/soc/mxs/mxs-saif.c
@@ -523,16 +523,24 @@ static int mxs_saif_trigger(struct snd_pcm_substream *substream, int cmd,
 
                 if (substream->stream == SNDRV_PCM_STREAM_PLAYBACK) {
                         /*
-                         * write a data to saif data register to trigger
-                         * the transfer
+                         * write data to saif data register to trigger
+                         * the transfer.
+                         * For 24-bit format the 32-bit FIFO register stores
+                         * only one channel, so we need to write twice.
+                         * This is also safe for the other non 24-bit formats.
                          */
                         __raw_writel(0, saif->base + SAIF_DATA);
+                        __raw_writel(0, saif->base + SAIF_DATA);
                 } else {
                         /*
-                         * read a data from saif data register to trigger
-                         * the receive
+                         * read data from saif data register to trigger
+                         * the receive.
+                         * For 24-bit format the 32-bit FIFO register stores
+                         * only one channel, so we need to read twice.
+                         * This is also safe for the other non 24-bit formats.
                          */
                         __raw_readl(saif->base + SAIF_DATA);
+                        __raw_readl(saif->base + SAIF_DATA);
                 }
 
                 master_saif->ongoing = 1;