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-rw-r--r--sound/soc/fsl/fsl_ssi.c74
1 files changed, 53 insertions, 21 deletions
diff --git a/sound/soc/fsl/fsl_ssi.c b/sound/soc/fsl/fsl_ssi.c
index 50349437d961..fde08660b63b 100644
--- a/sound/soc/fsl/fsl_ssi.c
+++ b/sound/soc/fsl/fsl_ssi.c
@@ -224,6 +224,12 @@ struct fsl_ssi_soc_data {
* @dbg_stats: Debugging statistics
*
* @soc: SoC specific data
+ *
+ * @fifo_watermark: the FIFO watermark setting. Notifies DMA when
+ * there are @fifo_watermark or fewer words in TX fifo or
+ * @fifo_watermark or more empty words in RX fifo.
+ * @dma_maxburst: max number of words to transfer in one go. So far,
+ * this is always the same as fifo_watermark.
*/
struct fsl_ssi_private {
struct regmap *regs;
@@ -263,6 +269,9 @@ struct fsl_ssi_private {
const struct fsl_ssi_soc_data *soc;
struct device *dev;
+
+ u32 fifo_watermark;
+ u32 dma_maxburst;
};
/*
@@ -1051,21 +1060,7 @@ static int _fsl_ssi_set_dai_fmt(struct device *dev,
regmap_write(regs, CCSR_SSI_SRCR, srcr);
regmap_write(regs, CCSR_SSI_SCR, scr);
- /*
- * Set the watermark for transmit FIFI 0 and receive FIFO 0. We don't
- * use FIFO 1. We program the transmit water to signal a DMA transfer
- * if there are only two (or fewer) elements left in the FIFO. Two
- * elements equals one frame (left channel, right channel). This value,
- * however, depends on the depth of the transmit buffer.
- *
- * We set the watermark on the same level as the DMA burstsize. For
- * fiq it is probably better to use the biggest possible watermark
- * size.
- */
- if (ssi_private->use_dma)
- wm = ssi_private->fifo_depth - 2;
- else
- wm = ssi_private->fifo_depth;
+ wm = ssi_private->fifo_watermark;
regmap_write(regs, CCSR_SSI_SFCSR,
CCSR_SSI_SFCSR_TFWM0(wm) | CCSR_SSI_SFCSR_RFWM0(wm) |
@@ -1373,12 +1368,8 @@ static int fsl_ssi_imx_probe(struct platform_device *pdev,
dev_dbg(&pdev->dev, "could not get baud clock: %ld\n",
PTR_ERR(ssi_private->baudclk));
- /*
- * We have burstsize be "fifo_depth - 2" to match the SSI
- * watermark setting in fsl_ssi_startup().
- */
- ssi_private->dma_params_tx.maxburst = ssi_private->fifo_depth - 2;
- ssi_private->dma_params_rx.maxburst = ssi_private->fifo_depth - 2;
+ ssi_private->dma_params_tx.maxburst = ssi_private->dma_maxburst;
+ ssi_private->dma_params_rx.maxburst = ssi_private->dma_maxburst;
ssi_private->dma_params_tx.addr = ssi_private->ssi_phys + CCSR_SSI_STX0;
ssi_private->dma_params_rx.addr = ssi_private->ssi_phys + CCSR_SSI_SRX0;
@@ -1543,6 +1534,47 @@ static int fsl_ssi_probe(struct platform_device *pdev)
/* Older 8610 DTs didn't have the fifo-depth property */
ssi_private->fifo_depth = 8;
+ /*
+ * Set the watermark for transmit FIFO 0 and receive FIFO 0. We don't
+ * use FIFO 1 but set the watermark appropriately nontheless.
+ * We program the transmit water to signal a DMA transfer
+ * if there are N elements left in the FIFO. For chips with 15-deep
+ * FIFOs, set watermark to 8. This allows the SSI to operate at a
+ * high data rate without channel slipping. Behavior is unchanged
+ * for the older chips with a fifo depth of only 8. A value of 4
+ * might be appropriate for the older chips, but is left at
+ * fifo_depth-2 until sombody has a chance to test.
+ *
+ * We set the watermark on the same level as the DMA burstsize. For
+ * fiq it is probably better to use the biggest possible watermark
+ * size.
+ */
+ switch (ssi_private->fifo_depth) {
+ case 15:
+ /*
+ * 2 samples is not enough when running at high data
+ * rates (like 48kHz @ 16 bits/channel, 16 channels)
+ * 8 seems to split things evenly and leave enough time
+ * for the DMA to fill the FIFO before it's over/under
+ * run.
+ */
+ ssi_private->fifo_watermark = 8;
+ ssi_private->dma_maxburst = 8;
+ break;
+ case 8:
+ default:
+ /*
+ * maintain old behavior for older chips.
+ * Keeping it the same because I don't have an older
+ * board to test with.
+ * I suspect this could be changed to be something to
+ * leave some more space in the fifo.
+ */
+ ssi_private->fifo_watermark = ssi_private->fifo_depth - 2;
+ ssi_private->dma_maxburst = ssi_private->fifo_depth - 2;
+ break;
+ }
+
dev_set_drvdata(&pdev->dev, ssi_private);
if (ssi_private->soc->imx) {