[RFC PATCH 3/7] ASoC: sunxi: sun4i-i2s: Prepare for runtime channel slot selection

[John Watts]

The sun4i I2S controller supports mapping channels to specific TDM
slots. This is usually done in a 1:1 mapping because there's not
really a reason to re-order the TDM slots in software.

On the R329 and D1 multiplexing can be done using pins as well as
TDM. Here's an example of using 3 pins and 2 slots (left and right):

Channel 0 -> DIN0 -> ADC0, TDM slot 0
Channel 1 -> DIN0 -> ADC0, TDM slot 1
Channel 2 -> DIN1 -> ADC1, TDM slot 0
Channel 3 -> DIN1 -> ADC1, TDM slot 1
Channel 4 -> DIN2 -> ADC2, TDM slot 0
Channel 5 -> DIN2 -> ADC2, TDM slot 1

This connects 3 separate TDM-unaware ADCs to the I2S controller.
Likewise, multiple TDM slots could be used to run two sets of
TDM-aware ADCs on one I2S controller.

Prepare for configurable slot selection by adding a channel to slot
mapping array and using that in the R329 code if we multiple DIN pins.

Signed-off-by: John Watts <contact@xxxxxxxxxx>
---
 sound/soc/sunxi/sun4i-i2s.c | 19 ++++++++++++++++++-
 1 file changed, 18 insertions(+), 1 deletion(-)

diff --git a/sound/soc/sunxi/sun4i-i2s.c b/sound/soc/sunxi/sun4i-i2s.c
index cf66f21646a4..627bf319e1cc 100644
--- a/sound/soc/sunxi/sun4i-i2s.c
+++ b/sound/soc/sunxi/sun4i-i2s.c
@@ -217,6 +217,7 @@ struct sun4i_i2s {
 	unsigned int	slots;
 	unsigned int	slot_width;
 	u8	channel_dins[16];
+	u8	channel_slots[16];
 
 	struct snd_dmaengine_dai_dma_data	capture_dma_data;
 	struct snd_dmaengine_dai_dma_data	playback_dma_data;
@@ -266,6 +267,17 @@ static int sun4i_i2s_read_channel_dins(struct device *dev, struct sun4i_i2s *i2s
 	return 0;
 }
 
+static int sun4i_i2s_read_channel_slots(struct device *dev, struct sun4i_i2s *i2s)
+{
+	int max_channels = ARRAY_SIZE(i2s->channel_dins);
+
+	/* Use a 1:1 mapping by default */
+	for (int i = 0; i < max_channels; ++i)
+		i2s->channel_slots[i] = i;
+
+	return 0;
+}
+
 static const struct sun4i_i2s_clk_div sun4i_i2s_bclk_div[] = {
 	{ .div = 2, .val = 0 },
 	{ .div = 4, .val = 1 },
@@ -570,7 +582,7 @@ static void sun50i_h6_write_channel_map(const struct sun4i_i2s *i2s,
 	for (int i = 3; i >= 0; i--) {
 		int channel = channel_start + i;
 		u8 din = i2s->channel_dins[channel];
-		u8 slot = channel; /* Map slot to channel */
+		u8 slot = i2s->channel_slots[channel];
 
 		reg_value <<= 8;
 		reg_value |= (din << 4) | slot;
@@ -1616,6 +1628,11 @@ static int sun4i_i2s_probe(struct platform_device *pdev)
 		return -EINVAL;
 	}
 
+	if (sun4i_i2s_read_channel_slots(&pdev->dev, i2s)) {
+		dev_err(&pdev->dev, "Invalid channel slots\n");
+		return -EINVAL;
+	}
+
 	i2s->playback_dma_data.addr = res->start +
 					i2s->variant->reg_offset_txdata;
 	i2s->playback_dma_data.maxburst = 8;
-- 
2.41.0