[alsa-devel] fsl_ssi.c: Getting channel slips with fsl_ssi.c in TDM (network) mode.

[Nicolin Chen]

On Thu, Oct 29, 2015 at 07:55:59AM -0700, Caleb Crome wrote:

> >> Therefore, if setting watermark to 8, each FIFO has 7 (15 - 8) space
> >> left, the largest safe burst size could be 14 (7 * 2) actually.

> > Oh, does this depend on the data size?  I'm using 16-bit data, so I
> > guess the bursts are measured in 2 byte units?  Does this mean that
> > the burst size should be dynamically adjusted depending on word size
> > (I guess done in hw_params)?

You don't need to do that. It's already been taken care in the DMA
code.

> Okay, so wm=8 and maxburst=14 definitely does not work at all,.  wm=8,
> maxburst=8 works okay, but still not perfect.

Make sure you are using Dual FIFO configurations for both SDMA and
SSI. You can refer to my change below (I've tested it with a two-
channel test case being played in 44.1KHz 16-bit):

diff --git a/arch/arm/boot/dts/imx6sx.dtsi b/arch/arm/boot/dts/imx6sx.dtsi
index b8a5056..f4c7308 100644
--- a/arch/arm/boot/dts/imx6sx.dtsi
+++ b/arch/arm/boot/dts/imx6sx.dtsi
@@ -307,7 +307,7 @@
 					clocks = <&clks IMX6SX_CLK_SSI1_IPG>,
 						 <&clks IMX6SX_CLK_SSI1>;
 					clock-names = "ipg", "baud";
-					dmas = <&sdma 37 1 0>, <&sdma 38 1 0>;
+					dmas = <&sdma 37 22 0>, <&sdma 38 22 0>;
 					dma-names = "rx", "tx";
 					fsl,fifo-depth = <15>;
 					status = "disabled";
@@ -321,7 +321,7 @@
 					clocks = <&clks IMX6SX_CLK_SSI2_IPG>,
 						 <&clks IMX6SX_CLK_SSI2>;
 					clock-names = "ipg", "baud";
-					dmas = <&sdma 41 1 0>, <&sdma 42 1 0>;
+					dmas = <&sdma 41 22 0>, <&sdma 42 22 0>;
 					dma-names = "rx", "tx";
 					fsl,fifo-depth = <15>;
 					status = "disabled";
@@ -335,7 +335,7 @@
 					clocks = <&clks IMX6SX_CLK_SSI3_IPG>,
 						 <&clks IMX6SX_CLK_SSI3>;
 					clock-names = "ipg", "baud";
-					dmas = <&sdma 45 1 0>, <&sdma 46 1 0>;
+					dmas = <&sdma 45 22 0>, <&sdma 46 22 0>;
 					dma-names = "rx", "tx";
 					fsl,fifo-depth = <15>;
 					status = "disabled";
diff --git a/sound/soc/fsl/fsl_ssi.c b/sound/soc/fsl/fsl_ssi.c
index 674abf7..7cfe661 100644
--- a/sound/soc/fsl/fsl_ssi.c
+++ b/sound/soc/fsl/fsl_ssi.c
@@ -1002,8 +1002,8 @@ static int _fsl_ssi_set_dai_fmt(struct device *dev,
 		wm = ssi_private->fifo_depth;
 
 	regmap_write(regs, CCSR_SSI_SFCSR,
-			CCSR_SSI_SFCSR_TFWM0(wm) | CCSR_SSI_SFCSR_RFWM0(wm) |
-			CCSR_SSI_SFCSR_TFWM1(wm) | CCSR_SSI_SFCSR_RFWM1(wm));
+			CCSR_SSI_SFCSR_TFWM0(8) | CCSR_SSI_SFCSR_RFWM0(8) |
+			CCSR_SSI_SFCSR_TFWM1(8) | CCSR_SSI_SFCSR_RFWM1(8));
 
 	if (ssi_private->use_dual_fifo) {
 		regmap_update_bits(regs, CCSR_SSI_SRCR, CCSR_SSI_SRCR_RFEN1,
@@ -1322,8 +1322,9 @@ static int fsl_ssi_imx_probe(struct platform_device *pdev,
 		/* When using dual fifo mode, we need to keep watermark
 		 * as even numbers due to dma script limitation.
 		 */
-		ssi_private->dma_params_tx.maxburst &= ~0x1;
-		ssi_private->dma_params_rx.maxburst &= ~0x1;
+		dev_info(&pdev->dev, "tunning burst size for Dual FIFO mode\n");
+		ssi_private->dma_params_tx.maxburst = 16;
+		ssi_private->dma_params_rx.maxburst = 16;
 	}
 
 	if (!ssi_private->use_dma) {

And make sure you have the dev_info() printed out in your console.
/* 22 in the DT is to call the Dual FIFO SDMA script */

> It started with:
> 
> frame 0:  00, 00, 10, 20, 30, 40, 50, 60, 70, 80, 90, a0, b0, c0, d0, e0
> frame 1:  f0, 01, 11, 21, 31, 41, 51, 61, 71, 81, 91, a1, b1, c1, d1, e1

If this happens, just try to let SDMA work before SSI starts to
read FIFOs -- enabling TDMAE or RDMAE before enabling TE or RE:

@@ -1093,6 +1093,15 @@ static int fsl_ssi_trigger(struct snd_pcm_substream *substream, int cmd,
 	case SNDRV_PCM_TRIGGER_RESUME:
 	case SNDRV_PCM_TRIGGER_PAUSE_RELEASE:
 		if (substream->stream == SNDRV_PCM_STREAM_PLAYBACK)
+			regmap_update_bits(regs, CCSR_SSI_SIER,
+					   CCSR_SSI_SIER_TDMAE,
+					   CCSR_SSI_SIER_TDMAE);
+		else
+			regmap_update_bits(regs, CCSR_SSI_SIER,
+					   CCSR_SSI_SIER_RDMAE,
+					   CCSR_SSI_SIER_RDMAE);
+
+		if (substream->stream == SNDRV_PCM_STREAM_PLAYBACK)
 			fsl_ssi_tx_config(ssi_private, true);
 		else
 			fsl_ssi_rx_config(ssi_private, true);

Nicolin