drivers: audio: dmic_mcux: remove arbitrary mapping of pdm to dmic channel

The dmic_mcux driver required a mapping of paired dmics to
specify the same pdm number, and would arbitrarily assign the left
channel of the pair to even dmic channel number and the right
to an odd dmic channel number.

Change this so that the pdm number in the mapping is
used as the dmic channel number, and paired dmics are checked to
specify consecutive pdm numbers (instead of the
same pdm number).

This allows users to control explicitly which dmic
channel to use and whether that dmic channel is left or right,
without this arbitrary indirect mapping. This is important
in case they want a dmic that is wired to be right channel
to be assigned to dmic channel 0, which is the only channel
that supports hwvad.

Signed-off-by: Mike J. Chen <mjchen@google.com>

Author: mjchen0

drivers/audio/dmic_mcux.c

@@ -67,18 +67,11 @@ static uint8_t dmic_mcux_hw_chan(struct mcux_dmic_drv_data *drv_data,
 	enum pdm_lr lr;
 	uint8_t hw_chan;
 
-	/* This function assigns hardware channel "n" to the left channel,
-	 * and hardware channel "n+1" to the right channel. This choice is
-	 * arbitrary, but must be followed throughout the driver.
-	 */
 	dmic_parse_channel_map(drv_data->chan_map_lo,
 			       drv_data->chan_map_hi,
 			       log_chan, &hw_chan, &lr);
-	if (lr == PDM_CHAN_LEFT) {
-		return hw_chan * 2;
-	} else {
-		return (hw_chan * 2) + 1;
-	}
+
+	return hw_chan;
 }
 
 static void dmic_mcux_activate_channels(struct mcux_dmic_drv_data *drv_data,
@@ -501,9 +494,9 @@ static int dmic_mcux_configure(const struct device *dev,
 			dmic_parse_channel_map(channel->req_chan_map_lo,
 					       channel->req_chan_map_hi,
 					       chan + 1, &hw_chan_1, &lr_1);
-			/* Verify that paired channels use same hardware index */
+			/* Verify that paired channels use consecutive hardware index */
 			if ((lr_0 == lr_1) ||
-			    (hw_chan_0 != hw_chan_1)) {
+			    (hw_chan_1 != (hw_chan_0 + 1))) {
 				return -EINVAL;
 			}
 		}