linux-kernel - [PATCH 2/2] iio: accel: bmc150: optimize i2c transfers in trigger handler

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Message-Id: <1424110621-16571-3-git-send-email-irina.tirdea@intel.com>
Date:	Mon, 16 Feb 2015 20:17:01 +0200
From:	Irina Tirdea <irina.tirdea@...el.com>
To:	Jonathan Cameron <jic23@...nel.org>, linux-iio@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org,
	Srinivas Pandruvada <srinivas.pandruvada@...el.com>,
	Adriana Reus <adriana.reus@...el.com>,
	Irina Tirdea <irina.tirdea@...el.com>
Subject: [PATCH 2/2] iio: accel: bmc150: optimize i2c transfers in trigger handler

Some i2c busses (e.g.: Synopsys DesignWare I2C adapter) need to
enable/disable the bus at each i2c transfer and must wait for
the enable/disable to happen before sending the data.

When reading data in the trigger handler, the bmc150 accel driver does
one i2c transfer for each axis. This has an impact on the frequency
of the accelerometer at high sample rates due to additional delays
introduced by the i2c bus at each transfer.

Reading all axis values in one i2c transfer reduces the delays
introduced by the i2c bus. In case i2c block read is not supported,
fallback to reading each axis as a separate word.

Signed-off-by: Irina Tirdea <irina.tirdea@...el.com>
Reviewed-by: Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>
---
 drivers/iio/accel/bmc150-accel.c | 44 +++++++++++++++++++++++++++++++---------
 1 file changed, 34 insertions(+), 10 deletions(-)

diff --git a/drivers/iio/accel/bmc150-accel.c b/drivers/iio/accel/bmc150-accel.c
index 2eb0102..db2e362 100644
--- a/drivers/iio/accel/bmc150-accel.c
+++ b/drivers/iio/accel/bmc150-accel.c
@@ -163,6 +163,8 @@ struct bmc150_accel_data {
 	bool motion_trigger_on;
 	int64_t timestamp;
 	const struct bmc150_accel_chip_info *chip_info;
+	s32 (*read_block_data)(const struct i2c_client *client, u8 command,
+			       u8 length, u8 *values);
 };
 
 static const struct {
@@ -206,6 +208,22 @@ static const struct {
 				       {500000, BMC150_ACCEL_SLEEP_500_MS},
 				       {1000000, BMC150_ACCEL_SLEEP_1_SEC} };
 
+static s32 bmc150_accel_read_block_data(const struct i2c_client *client,
+					u8 command, u8 length, u8 *values)
+{
+	s32 data;
+	u8 i;
+
+	for (i = 0; i < length; i += 2) {
+		data = i2c_smbus_read_word_data(client, command + i);
+		if (data < 0)
+			return data;
+
+		values[i] = data & 0xFF;
+		values[i+1] = data >> 8;
+	}
+	return i;
+}
 
 static int bmc150_accel_set_mode(struct bmc150_accel_data *data,
 				 enum bmc150_power_modes mode,
@@ -929,19 +947,14 @@ static irqreturn_t bmc150_accel_trigger_handler(int irq, void *p)
 	struct iio_poll_func *pf = p;
 	struct iio_dev *indio_dev = pf->indio_dev;
 	struct bmc150_accel_data *data = iio_priv(indio_dev);
-	int bit, ret, i = 0;
+	int ret;
 
 	mutex_lock(&data->mutex);
-	for (bit = 0; bit < AXIS_MAX; bit++) {
-		ret = i2c_smbus_read_word_data(data->client,
-					       BMC150_ACCEL_AXIS_TO_REG(bit));
-		if (ret < 0) {
-			mutex_unlock(&data->mutex);
-			goto err_read;
-		}
-		data->buffer[i++] = ret;
-	}
+	ret = data->read_block_data(data->client, BMC150_ACCEL_REG_XOUT_L,
+				    AXIS_MAX * 2, (u8 *) data->buffer);
 	mutex_unlock(&data->mutex);
+	if (ret < 0)
+		goto err_read;
 
 	iio_push_to_buffers_with_timestamp(indio_dev, data->buffer,
 					   data->timestamp);
@@ -1153,6 +1166,11 @@ static int bmc150_accel_probe(struct i2c_client *client,
 	const char *name = NULL;
 	int chip_id = 0;
 
+	if (!i2c_check_functionality(client->adapter,
+				     I2C_FUNC_SMBUS_BYTE_DATA |
+				     I2C_FUNC_SMBUS_READ_WORD_DATA))
+		return -ENODEV;
+
 	indio_dev = devm_iio_device_alloc(&client->dev, sizeof(*data));
 	if (!indio_dev)
 		return -ENOMEM;
@@ -1161,6 +1179,12 @@ static int bmc150_accel_probe(struct i2c_client *client,
 	i2c_set_clientdata(client, indio_dev);
 	data->client = client;
 
+	if (i2c_check_functionality(client->adapter,
+				    I2C_FUNC_SMBUS_READ_I2C_BLOCK))
+		data->read_block_data = i2c_smbus_read_i2c_block_data;
+	else
+		data->read_block_data = bmc150_accel_read_block_data;
+
 	if (id) {
 		name = id->name;
 		chip_id = id->driver_data;
-- 
1.9.1

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