ASoC: bcm2835: Add support for TDM modes

bcm2835 supports arbitrary positioning of channel data within
a frame and thus is capable of supporting TDM modes. Since
the driver is limited to 2-channel operations only TDM setups
with exactly 2 active slots are supported.

Logical TDM slot numbering follows the usual convention:

For I2S-like modes, with a 50% duty-cycle frame clock,
slots 0, 2, ... are transmitted in the first half of a frame,
slots 1, 3, ... are transmitted in the second half.

For DSP modes slot numbering is ascending: 0, 1, 2, 3, ...

Channel position calculation has been refactored to use
TDM info and moved out of hw_params.

set_tdm_slot, set_bclk_ratio and hw_params now check more
strictly if the configuration is valid. Illegal configurations
like odd number of slots in I2S mode, data lengths exceeding
slot width or frame sizes larger than the hardware limit of
1024 are rejected. Also hw_params now properly checks for
errors from clk_set_rate.

Allowed PCM formats are already guarded by stream constraints,
thus the formats check in hw_params has been removed and
data_length is now retrieved via params_width().

Also standard functions like snd_soc_params_to_bclk are now
being used instead of manual calculations to make the code
more readable.

Special care has been taken to ensure that set_bclk_ratio works
as before. The bclk ratio is mapped to a 2-channel TDM config
with a slot width of half the ratio. In order to support odd ratios,
which can't be expressed via a TDM config, the ratio (frame length)
is stored and used by hw_params.
Signed-off-by: Matthias Reichl <hias@horus.com>
Signed-off-by: Mark Brown <broonie@kernel.org>

sound/soc/bcm/bcm2835-i2s.c

@@ -31,6 +31,7 @@
  * General Public License for more details.
  */
 
+#include <linux/bitops.h>
 #include <linux/clk.h>
 #include <linux/delay.h>
 #include <linux/device.h>
@@ -99,6 +100,8 @@
 #define BCM2835_I2S_CHWID(v)		(v)
 #define BCM2835_I2S_CH1(v)		((v) << 16)
 #define BCM2835_I2S_CH2(v)		(v)
+#define BCM2835_I2S_CH1_POS(v)		BCM2835_I2S_CH1(BCM2835_I2S_CHPOS(v))
+#define BCM2835_I2S_CH2_POS(v)		BCM2835_I2S_CH2(BCM2835_I2S_CHPOS(v))
 
 #define BCM2835_I2S_TX_PANIC(v)	((v) << 24)
 #define BCM2835_I2S_RX_PANIC(v)	((v) << 16)
@@ -110,12 +113,19 @@
 #define BCM2835_I2S_INT_RXR		BIT(1)
 #define BCM2835_I2S_INT_TXW		BIT(0)
 
+/* Frame length register is 10 bit, maximum length 1024 */
+#define BCM2835_I2S_MAX_FRAME_LENGTH	1024
+
 /* General device struct */
 struct bcm2835_i2s_dev {
 	struct device				*dev;
 	struct snd_dmaengine_dai_dma_data	dma_data[2];
 	unsigned int				fmt;
-	unsigned int				bclk_ratio;
+	unsigned int				tdm_slots;
+	unsigned int				rx_mask;
+	unsigned int				tx_mask;
+	unsigned int				slot_width;
+	unsigned int				frame_length;
 
 	struct regmap				*i2s_regmap;
 	struct clk				*clk;
@@ -225,19 +235,117 @@ static int bcm2835_i2s_set_dai_bclk_ratio(struct snd_soc_dai *dai,
 				      unsigned int ratio)
 {
 	struct bcm2835_i2s_dev *dev = snd_soc_dai_get_drvdata(dai);
-	dev->bclk_ratio = ratio;
+
+	if (!ratio) {
+		dev->tdm_slots = 0;
+		return 0;
+	}
+
+	if (ratio > BCM2835_I2S_MAX_FRAME_LENGTH)
+		return -EINVAL;
+
+	dev->tdm_slots = 2;
+	dev->rx_mask = 0x03;
+	dev->tx_mask = 0x03;
+	dev->slot_width = ratio / 2;
+	dev->frame_length = ratio;
+
+	return 0;
+}
+
+static int bcm2835_i2s_set_dai_tdm_slot(struct snd_soc_dai *dai,
+	unsigned int tx_mask, unsigned int rx_mask,
+	int slots, int width)
+{
+	struct bcm2835_i2s_dev *dev = snd_soc_dai_get_drvdata(dai);
+
+	if (slots) {
+		if (slots < 0 || width < 0)
+			return -EINVAL;
+
+		/* Limit masks to available slots */
+		rx_mask &= GENMASK(slots - 1, 0);
+		tx_mask &= GENMASK(slots - 1, 0);
+
+		/*
+		 * The driver is limited to 2-channel setups.
+		 * Check that exactly 2 bits are set in the masks.
+		 */
+		if (hweight_long((unsigned long) rx_mask) != 2
+		    || hweight_long((unsigned long) tx_mask) != 2)
+			return -EINVAL;
+
+		if (slots * width > BCM2835_I2S_MAX_FRAME_LENGTH)
+			return -EINVAL;
+	}
+
+	dev->tdm_slots = slots;
+
+	dev->rx_mask = rx_mask;
+	dev->tx_mask = tx_mask;
+	dev->slot_width = width;
+	dev->frame_length = slots * width;
+
 	return 0;
 }
 
+/*
+ * Convert logical slot number into physical slot number.
+ *
+ * If odd_offset is 0 sequential number is identical to logical number.
+ * This is used for DSP modes with slot numbering 0 1 2 3 ...
+ *
+ * Otherwise odd_offset defines the physical offset for odd numbered
+ * slots. This is used for I2S and left/right justified modes to
+ * translate from logical slot numbers 0 1 2 3 ... into physical slot
+ * numbers 0 2 ... 3 4 ...
+ */
+static int bcm2835_i2s_convert_slot(unsigned int slot, unsigned int odd_offset)
+{
+	if (!odd_offset)
+		return slot;
+
+	if (slot & 1)
+		return (slot >> 1) + odd_offset;
+
+	return slot >> 1;
+}
+
+/*
+ * Calculate channel position from mask and slot width.
+ *
+ * Mask must contain exactly 2 set bits.
+ * Lowest set bit is channel 1 position, highest set bit channel 2.
+ * The constant offset is added to both channel positions.
+ *
+ * If odd_offset is > 0 slot positions are translated to
+ * I2S-style TDM slot numbering ( 0 2 ... 3 4 ...) with odd
+ * logical slot numbers starting at physical slot odd_offset.
+ */
+static void bcm2835_i2s_calc_channel_pos(
+	unsigned int *ch1_pos, unsigned int *ch2_pos,
+	unsigned int mask, unsigned int width,
+	unsigned int bit_offset, unsigned int odd_offset)
+{
+	*ch1_pos = bcm2835_i2s_convert_slot((ffs(mask) - 1), odd_offset)
+			* width + bit_offset;
+	*ch2_pos = bcm2835_i2s_convert_slot((fls(mask) - 1), odd_offset)
+			* width + bit_offset;
+}
+
 static int bcm2835_i2s_hw_params(struct snd_pcm_substream *substream,
 				 struct snd_pcm_hw_params *params,
 				 struct snd_soc_dai *dai)
 {
 	struct bcm2835_i2s_dev *dev = snd_soc_dai_get_drvdata(dai);
-	unsigned int sampling_rate = params_rate(params);
-	unsigned int data_length, data_delay, bclk_ratio;
-	unsigned int ch1pos, ch2pos, mode, format;
+	unsigned int data_length, data_delay, framesync_length;
+	unsigned int slots, slot_width, odd_slot_offset;
+	int frame_length, bclk_rate;
+	unsigned int rx_mask, tx_mask;
+	unsigned int rx_ch1_pos, rx_ch2_pos, tx_ch1_pos, tx_ch2_pos;
+	unsigned int mode, format;
 	uint32_t csreg;
+	int ret = 0;
 
 	/*
 	 * If a stream is already enabled,
@@ -248,39 +356,44 @@ static int bcm2835_i2s_hw_params(struct snd_pcm_substream *substream,
 	if (csreg & (BCM2835_I2S_TXON | BCM2835_I2S_RXON))
 		return 0;
 
-	/*
-	 * Adjust the data length according to the format.
-	 * We prefill the half frame length with an integer
-	 * divider of 2400 as explained at the clock settings.
-	 * Maybe it is overwritten there, if the Integer mode
-	 * does not apply.
-	 */
-	switch (params_format(params)) {
-	case SNDRV_PCM_FORMAT_S16_LE:
-		data_length = 16;
-		break;
-	case SNDRV_PCM_FORMAT_S24_LE:
-		data_length = 24;
-		break;
-	case SNDRV_PCM_FORMAT_S32_LE:
-		data_length = 32;
-		break;
-	default:
-		return -EINVAL;
+	data_length = params_width(params);
+	data_delay = 0;
+	odd_slot_offset = 0;
+	mode = 0;
+
+	if (dev->tdm_slots) {
+		slots = dev->tdm_slots;
+		slot_width = dev->slot_width;
+		frame_length = dev->frame_length;
+		rx_mask = dev->rx_mask;
+		tx_mask = dev->tx_mask;
+		bclk_rate = dev->frame_length * params_rate(params);
+	} else {
+		slots = 2;
+		slot_width = params_width(params);
+		rx_mask = 0x03;
+		tx_mask = 0x03;
+
+		frame_length = snd_soc_params_to_frame_size(params);
+		if (frame_length < 0)
+			return frame_length;
+
+		bclk_rate = snd_soc_params_to_bclk(params);
+		if (bclk_rate < 0)
+			return bclk_rate;
 	}
 
-	/* If bclk_ratio already set, use that one. */
-	if (dev->bclk_ratio)
-		bclk_ratio = dev->bclk_ratio;
-	else
-		/* otherwise calculate a fitting block ratio */
-		bclk_ratio = 2 * data_length;
+	/* Check if data fits into slots */
+	if (data_length > slot_width)
+		return -EINVAL;
 
 	/* Clock should only be set up here if CPU is clock master */
 	switch (dev->fmt & SND_SOC_DAIFMT_MASTER_MASK) {
 	case SND_SOC_DAIFMT_CBS_CFS:
 	case SND_SOC_DAIFMT_CBS_CFM:
-		clk_set_rate(dev->clk, sampling_rate * bclk_ratio);
+		ret = clk_set_rate(dev->clk, bclk_rate);
+		if (ret)
+			return ret;
 		break;
 	default:
 		break;
@@ -294,9 +407,26 @@ static int bcm2835_i2s_hw_params(struct snd_pcm_substream *substream,
 
 	format |= BCM2835_I2S_CHWID((data_length-8)&0xf);
 
+	/* CH2 format is the same as for CH1 */
+	format = BCM2835_I2S_CH1(format) | BCM2835_I2S_CH2(format);
+
 	switch (dev->fmt & SND_SOC_DAIFMT_FORMAT_MASK) {
 	case SND_SOC_DAIFMT_I2S:
+		/* I2S mode needs an even number of slots */
+		if (slots & 1)
+			return -EINVAL;
+
+		/*
+		 * Use I2S-style logical slot numbering: even slots
+		 * are in first half of frame, odd slots in second half.
+		 */
+		odd_slot_offset = slots >> 1;
+
+		/* MSB starts one cycle after frame start */
 		data_delay = 1;
+
+		/* Setup frame sync signal for 50% duty cycle */
+		framesync_length = frame_length / 2;
 		break;
 	default:
 		/*
@@ -307,18 +437,10 @@ static int bcm2835_i2s_hw_params(struct snd_pcm_substream *substream,
 		return -EINVAL;
 	}
 
-	ch1pos = data_delay;
-	ch2pos = bclk_ratio / 2 + data_delay;
-
-	switch (params_channels(params)) {
-	case 2:
-		format = BCM2835_I2S_CH1(format) | BCM2835_I2S_CH2(format);
-		format |= BCM2835_I2S_CH1(BCM2835_I2S_CHPOS(ch1pos));
-		format |= BCM2835_I2S_CH2(BCM2835_I2S_CHPOS(ch2pos));
-		break;
-	default:
-		return -EINVAL;
-	}
+	bcm2835_i2s_calc_channel_pos(&rx_ch1_pos, &rx_ch2_pos,
+		rx_mask, slot_width, data_delay, odd_slot_offset);
+	bcm2835_i2s_calc_channel_pos(&tx_ch1_pos, &tx_ch2_pos,
+		tx_mask, slot_width, data_delay, odd_slot_offset);
 
 	/*
 	 * Set format for both streams.
@@ -326,11 +448,16 @@ static int bcm2835_i2s_hw_params(struct snd_pcm_substream *substream,
 	 * (and therefore word length) anyway,
 	 * so the format will be the same.
 	 */
-	regmap_write(dev->i2s_regmap, BCM2835_I2S_RXC_A_REG, format);
-	regmap_write(dev->i2s_regmap, BCM2835_I2S_TXC_A_REG, format);
+	regmap_write(dev->i2s_regmap, BCM2835_I2S_RXC_A_REG, 
+		  format
+		| BCM2835_I2S_CH1_POS(rx_ch1_pos)
+		| BCM2835_I2S_CH2_POS(rx_ch2_pos));
+	regmap_write(dev->i2s_regmap, BCM2835_I2S_TXC_A_REG, 
+		  format
+		| BCM2835_I2S_CH1_POS(tx_ch1_pos)
+		| BCM2835_I2S_CH2_POS(tx_ch2_pos));
 
 	/* Setup the I2S mode */
-	mode = 0;
 
 	if (data_length <= 16) {
 		/*
@@ -342,8 +469,8 @@ static int bcm2835_i2s_hw_params(struct snd_pcm_substream *substream,
 		mode |= BCM2835_I2S_FTXP | BCM2835_I2S_FRXP;
 	}
 
-	mode |= BCM2835_I2S_FLEN(bclk_ratio - 1);
-	mode |= BCM2835_I2S_FSLEN(bclk_ratio / 2);
+	mode |= BCM2835_I2S_FLEN(frame_length - 1);
+	mode |= BCM2835_I2S_FSLEN(framesync_length);
 
 	/* Master or slave? */
 	switch (dev->fmt & SND_SOC_DAIFMT_MASTER_MASK) {
@@ -423,7 +550,20 @@ static int bcm2835_i2s_hw_params(struct snd_pcm_substream *substream,
 	/* Clear FIFOs */
 	bcm2835_i2s_clear_fifos(dev, true, true);
 
-	return 0;
+	dev_dbg(dev->dev,
+		"slots: %d width: %d rx mask: 0x%02x tx_mask: 0x%02x\n",
+		slots, slot_width, rx_mask, tx_mask);
+
+	dev_dbg(dev->dev, "frame len: %d sync len: %d data len: %d\n",
+		frame_length, framesync_length, data_length);
+
+	dev_dbg(dev->dev, "rx pos: %d,%d tx pos: %d,%d\n",
+		rx_ch1_pos, rx_ch2_pos, tx_ch1_pos, tx_ch2_pos);
+
+	dev_dbg(dev->dev, "sampling rate: %d bclk rate: %d\n",
+		params_rate(params), bclk_rate);
+
+	return ret;
 }
 
 static int bcm2835_i2s_prepare(struct snd_pcm_substream *substream,
@@ -559,6 +699,7 @@ static const struct snd_soc_dai_ops bcm2835_i2s_dai_ops = {
 	.hw_params	= bcm2835_i2s_hw_params,
 	.set_fmt	= bcm2835_i2s_set_dai_fmt,
 	.set_bclk_ratio	= bcm2835_i2s_set_dai_bclk_ratio,
+	.set_tdm_slot	= bcm2835_i2s_set_dai_tdm_slot,
 };
 
 static int bcm2835_i2s_dai_probe(struct snd_soc_dai *dai)
@@ -699,9 +840,6 @@ static int bcm2835_i2s_probe(struct platform_device *pdev)
 	dev->dma_data[SNDRV_PCM_STREAM_CAPTURE].flags =
 		SND_DMAENGINE_PCM_DAI_FLAG_PACK;
 
-	/* BCLK ratio - use default */
-	dev->bclk_ratio = 0;
-
 	/* Store the pdev */
 	dev->dev = &pdev->dev;
 	dev_set_drvdata(&pdev->dev, dev);