ASoC: fsl_sai: derive TX FIFO watermark from FIFO depth

The DMA request schould be triggered as soon as the FIFO has space
for another burst. As different versions of the SAI block have
different FIFO sizes, the watrmark level needs to be derived from
version specific data.
Signed-off-by: Lucas Stach <l.stach@pengutronix.de>
Tested-by: Angus Ainslie <angus@akkea.ca>
Reviewed-by: Angus Ainslie <angus@akkea.ca>
Link: https://lore.kernel.org/r/20190717105635.18514-3-l.stach@pengutronix.deSigned-off-by: Mark Brown <broonie@kernel.org>

sound/soc/fsl/fsl_sai.c

@@ -640,7 +640,7 @@ static int fsl_sai_dai_probe(struct snd_soc_dai *cpu_dai)
 	regmap_write(sai->regmap, FSL_SAI_RCSR, 0);
 
 	regmap_update_bits(sai->regmap, FSL_SAI_TCR1, FSL_SAI_CR1_RFW_MASK,
-			   FSL_SAI_MAXBURST_TX * 2);
+			   sai->soc_data->fifo_depth - FSL_SAI_MAXBURST_TX);
 	regmap_update_bits(sai->regmap, FSL_SAI_RCR1, FSL_SAI_CR1_RFW_MASK,
 			   FSL_SAI_MAXBURST_RX - 1);
 
@@ -913,10 +913,12 @@ static int fsl_sai_remove(struct platform_device *pdev)
 
 static const struct fsl_sai_soc_data fsl_sai_vf610_data = {
 	.use_imx_pcm = false,
+	.fifo_depth = 32,
 };
 
 static const struct fsl_sai_soc_data fsl_sai_imx6sx_data = {
 	.use_imx_pcm = true,
+	.fifo_depth = 32,
 };
 
 static const struct of_device_id fsl_sai_ids[] = {

sound/soc/fsl/fsl_sai.h

@@ -128,6 +128,7 @@
 
 struct fsl_sai_soc_data {
 	bool use_imx_pcm;
+	unsigned int fifo_depth;
 };
 
 struct fsl_sai {