iio: bu27008: Add illuminance channel

The RGB + IR data can be used to calculate the illuminance value (luxes).
Implement the equation obtained from the ROHM HW colleagues and add a
raw light data channel outputting illuminance values in (nano) Luxes.

Both the read_raw and buffering values are supported, with the limitation
that buffering is only allowed when a suitable scan-mask is used. (RGB+IR,
no clear).

The equation has been developed by ROHM HW colleagues for open air sensor.
Adding any lens to the sensor is likely to impact to used c1, c2, c3
coefficients. Also, the output values have only been tested on BU27008.

According to the HW colleagues, the very same equation should work on
BU27010 as well.

Calculate and output illuminance values from BU27008 and BU27010.
Signed-off-by: Matti Vaittinen <mazziesaccount@gmail.com>
Link: https://lore.kernel.org/r/ZTJcOxSb/WHzdN8h@dc78bmyyyyyyyyyyyyydt-3.rev.dnainternet.fiSigned-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/light/rohm-bu27008.c

@@ -130,6 +130,7 @@
  * @BU27008_BLUE:	Blue channel. Via data2 (when used).
  * @BU27008_CLEAR:	Clear channel. Via data2 or data3 (when used).
  * @BU27008_IR:		IR channel. Via data3 (when used).
+ * @BU27008_LUX:	Illuminance channel, computed using RGB and IR.
  * @BU27008_NUM_CHANS:	Number of channel types.
  */
 enum bu27008_chan_type {
@@ -138,6 +139,7 @@ enum bu27008_chan_type {
 	BU27008_BLUE,
 	BU27008_CLEAR,
 	BU27008_IR,
+	BU27008_LUX,
 	BU27008_NUM_CHANS
 };
 
@@ -172,6 +174,8 @@ static const unsigned long bu27008_scan_masks[] = {
 	ALWAYS_SCANNABLE | BIT(BU27008_CLEAR) | BIT(BU27008_IR),
 	/* buffer is R, G, B, IR */
 	ALWAYS_SCANNABLE | BIT(BU27008_BLUE) | BIT(BU27008_IR),
+	/* buffer is R, G, B, IR, LUX */
+	ALWAYS_SCANNABLE | BIT(BU27008_BLUE) | BIT(BU27008_IR) | BIT(BU27008_LUX),
 	0
 };
 
@@ -331,6 +335,19 @@ static const struct iio_chan_spec bu27008_channels[] = {
 	 * Hence we don't advertise available ones either.
 	 */
 	BU27008_CHAN(IR, DATA3, 0),
+	{
+		.type = IIO_LIGHT,
+		.info_mask_separate = BIT(IIO_CHAN_INFO_RAW) |
+				      BIT(IIO_CHAN_INFO_SCALE),
+		.channel = BU27008_LUX,
+		.scan_index = BU27008_LUX,
+		.scan_type = {
+			.sign = 'u',
+			.realbits = 64,
+			.storagebits = 64,
+			.endianness = IIO_CPU,
+		},
+	},
 	IIO_CHAN_SOFT_TIMESTAMP(BU27008_NUM_CHANS),
 };
 
@@ -1004,6 +1021,169 @@ static int bu27008_read_one(struct bu27008_data *data, struct iio_dev *idev,
 	return ret;
 }
 
+#define BU27008_LUX_DATA_RED	0
+#define BU27008_LUX_DATA_GREEN	1
+#define BU27008_LUX_DATA_BLUE	2
+#define BU27008_LUX_DATA_IR	3
+#define LUX_DATA_SIZE (BU27008_NUM_HW_CHANS * sizeof(__le16))
+
+static int bu27008_read_lux_chans(struct bu27008_data *data, unsigned int time,
+				  __le16 *chan_data)
+{
+	int ret, chan_sel, tmpret, valid;
+
+	chan_sel = BU27008_BLUE2_IR3 << (ffs(data->cd->chan_sel_mask) - 1);
+
+	ret = regmap_update_bits(data->regmap, data->cd->chan_sel_reg,
+				 data->cd->chan_sel_mask, chan_sel);
+	if (ret)
+		return ret;
+
+	ret = bu27008_meas_set(data, true);
+	if (ret)
+		return ret;
+
+	msleep(time / USEC_PER_MSEC);
+
+	ret = regmap_read_poll_timeout(data->regmap, data->cd->valid_reg,
+				       valid, (valid & BU27008_MASK_VALID),
+				       BU27008_VALID_RESULT_WAIT_QUANTA_US,
+				       BU27008_MAX_VALID_RESULT_WAIT_US);
+	if (ret)
+		goto out;
+
+	ret = regmap_bulk_read(data->regmap, BU27008_REG_DATA0_LO, chan_data,
+			       LUX_DATA_SIZE);
+	if (ret)
+		goto out;
+out:
+	tmpret = bu27008_meas_set(data, false);
+	if (tmpret)
+		dev_warn(data->dev, "Stopping measurement failed\n");
+
+	return ret;
+}
+
+/*
+ * Following equation for computing lux out of register values was given by
+ * ROHM HW colleagues;
+ *
+ * Red = RedData*1024 / Gain * 20 / meas_mode
+ * Green = GreenData* 1024 / Gain * 20 / meas_mode
+ * Blue = BlueData* 1024 / Gain * 20 / meas_mode
+ * IR = IrData* 1024 / Gain * 20 / meas_mode
+ *
+ * where meas_mode is the integration time in mS / 10
+ *
+ * IRratio = (IR > 0.18 * Green) ? 0 : 1
+ *
+ * Lx = max(c1*Red + c2*Green + c3*Blue,0)
+ *
+ * for
+ * IRratio 0: c1 = -0.00002237, c2 = 0.0003219, c3 = -0.000120371
+ * IRratio 1: c1 = -0.00001074, c2 = 0.000305415, c3 = -0.000129367
+ */
+
+/*
+ * The max chan data is 0xffff. When we multiply it by 1024 * 20, we'll get
+ * 0x4FFFB000 which still fits in 32-bit integer. This won't overflow.
+ */
+#define NORM_CHAN_DATA_FOR_LX_CALC(chan, gain, time) (le16_to_cpu(chan) * \
+				   1024 * 20 / (gain) / (time))
+static u64 bu27008_calc_nlux(struct bu27008_data *data, __le16 *lux_data,
+		unsigned int gain, unsigned int gain_ir, unsigned int time)
+{
+	unsigned int red, green, blue, ir;
+	s64 c1, c2, c3, nlux;
+
+	time /= 10000;
+	ir = NORM_CHAN_DATA_FOR_LX_CALC(lux_data[BU27008_LUX_DATA_IR], gain_ir, time);
+	red = NORM_CHAN_DATA_FOR_LX_CALC(lux_data[BU27008_LUX_DATA_RED], gain, time);
+	green = NORM_CHAN_DATA_FOR_LX_CALC(lux_data[BU27008_LUX_DATA_GREEN], gain, time);
+	blue = NORM_CHAN_DATA_FOR_LX_CALC(lux_data[BU27008_LUX_DATA_BLUE], gain, time);
+
+	if ((u64)ir * 100LLU > (u64)green * 18LLU) {
+		c1 = -22370;
+		c2 = 321900;
+		c3 = -120371;
+	} else {
+		c1 = -10740;
+		c2 = 305415;
+		c3 = -129367;
+	}
+	nlux = c1 * red + c2 * green + c3 * blue;
+
+	return max_t(s64, 0, nlux);
+}
+
+static int bu27008_get_time_n_gains(struct bu27008_data *data,
+		unsigned int *gain, unsigned int *gain_ir, unsigned int *time)
+{
+	int ret;
+
+	ret = bu27008_get_gain(data, &data->gts, gain);
+	if (ret < 0)
+		return ret;
+
+	ret = bu27008_get_gain(data, &data->gts_ir, gain_ir);
+	if (ret < 0)
+		return ret;
+
+	ret = bu27008_get_int_time_us(data);
+	if (ret < 0)
+		return ret;
+
+	/* Max integration time is 400000. Fits in signed int. */
+	*time = ret;
+
+	return 0;
+}
+
+struct bu27008_buf {
+	__le16 chan[BU27008_NUM_HW_CHANS];
+	u64 lux __aligned(8);
+	s64 ts __aligned(8);
+};
+
+static int bu27008_buffer_fill_lux(struct bu27008_data *data,
+				   struct bu27008_buf *raw)
+{
+	unsigned int gain, gain_ir, time;
+	int ret;
+
+	ret = bu27008_get_time_n_gains(data, &gain, &gain_ir, &time);
+	if (ret)
+		return ret;
+
+	raw->lux = bu27008_calc_nlux(data, raw->chan, gain, gain_ir, time);
+
+	return 0;
+}
+
+static int bu27008_read_lux(struct bu27008_data *data, struct iio_dev *idev,
+			    struct iio_chan_spec const *chan,
+			    int *val, int *val2)
+{
+	__le16 lux_data[BU27008_NUM_HW_CHANS];
+	unsigned int gain, gain_ir, time;
+	u64 nlux;
+	int ret;
+
+	ret = bu27008_get_time_n_gains(data, &gain, &gain_ir, &time);
+	if (ret)
+		return ret;
+
+	ret = bu27008_read_lux_chans(data, time, lux_data);
+	if (ret)
+		return ret;
+
+	nlux = bu27008_calc_nlux(data, lux_data, gain, gain_ir, time);
+	*val = (int)nlux;
+	*val2 = nlux >> 32LLU;
+
+	return IIO_VAL_INT_64;
+}
+
 static int bu27008_read_raw(struct iio_dev *idev,
 			   struct iio_chan_spec const *chan,
 			   int *val, int *val2, long mask)
@@ -1018,7 +1198,10 @@ static int bu27008_read_raw(struct iio_dev *idev,
 			return -EBUSY;
 
 		mutex_lock(&data->mutex);
-		ret = bu27008_read_one(data, idev, chan, val, val2);
+		if (chan->type == IIO_LIGHT)
+			ret = bu27008_read_lux(data, idev, chan, val, val2);
+		else
+			ret = bu27008_read_one(data, idev, chan, val, val2);
 		mutex_unlock(&data->mutex);
 
 		iio_device_release_direct_mode(idev);
@@ -1026,6 +1209,11 @@ static int bu27008_read_raw(struct iio_dev *idev,
 		return ret;
 
 	case IIO_CHAN_INFO_SCALE:
+		if (chan->type == IIO_LIGHT) {
+			*val = 0;
+			*val2 = 1;
+			return IIO_VAL_INT_PLUS_NANO;
+		}
 		ret = bu27008_get_scale(data, chan->scan_index == BU27008_IR,
 					val, val2);
 		if (ret)
@@ -1236,10 +1424,7 @@ static irqreturn_t bu27008_trigger_handler(int irq, void *p)
 	struct iio_poll_func *pf = p;
 	struct iio_dev *idev = pf->indio_dev;
 	struct bu27008_data *data = iio_priv(idev);
-	struct {
-		__le16 chan[BU27008_NUM_HW_CHANS];
-		s64 ts __aligned(8);
-	} raw;
+	struct bu27008_buf raw;
 	int ret, dummy;
 
 	memset(&raw, 0, sizeof(raw));
@@ -1257,6 +1442,12 @@ static irqreturn_t bu27008_trigger_handler(int irq, void *p)
 	if (ret < 0)
 		goto err_read;
 
+	if (test_bit(BU27008_LUX, idev->active_scan_mask)) {
+		ret = bu27008_buffer_fill_lux(data, &raw);
+		if (ret)
+			goto err_read;
+	}
+
 	iio_push_to_buffers_with_timestamp(idev, &raw, pf->timestamp);
 err_read:
 	iio_trigger_notify_done(idev->trig);