[v3 11/13] iio: imu: add BNO055 serdev driver

Andrea Merello
2022-02-17T16:27:43Z

This path adds a serdev driver for communicating to a BNO055 IMU via
serial bus, and it enables the BNO055 core driver to work in this
scenario.

Signed-off-by: Andrea Merello <andrea.merello@iit.it>
---
drivers/iio/imu/bno055/Kconfig | 10 +
drivers/iio/imu/bno055/Makefile | 1 +
drivers/iio/imu/bno055/bno055_sl.c | 557 +++++++++++++++++++++++++++++
3 files changed, 568 insertions(+)
create mode 100644 drivers/iio/imu/bno055/bno055_sl.c

diff --git a/drivers/iio/imu/bno055/Kconfig b/drivers/iio/imu/bno055/Kconfig
index d0ab3221fba5..8a83639ad2a9 100644
--- a/drivers/iio/imu/bno055/Kconfig
+++ b/drivers/iio/imu/bno055/Kconfig
@@ -2,3 +2,13 @@

config BOSCH_BNO055_IIO
tristate
+
+config BOSCH_BNO055_SERIAL
+ tristate "Bosch BNO055 attached via serial bus"
+ depends on SERIAL_DEV_BUS
+ select BOSCH_BNO055_IIO
+ help
+ Enable this to support Bosch BNO055 IMUs attached via serial bus.
+
+ This driver can also be built as a module. If so, the module will be
+ called bno055_sl.
diff --git a/drivers/iio/imu/bno055/Makefile b/drivers/iio/imu/bno055/Makefile
index 56cc4de60a7e..416f0ff96de5 100644
--- a/drivers/iio/imu/bno055/Makefile
+++ b/drivers/iio/imu/bno055/Makefile
@@ -1,3 +1,4 @@
# SPDX-License-Identifier: GPL-2.0

obj-$(CONFIG_BOSCH_BNO055_IIO) += bno055.o
+obj-$(CONFIG_BOSCH_BNO055_SERIAL) += bno055_sl.o
diff --git a/drivers/iio/imu/bno055/bno055_sl.c b/drivers/iio/imu/bno055/bno055_sl.c
new file mode 100644
index 000000000000..5af44f151389
--- /dev/null
+++ b/drivers/iio/imu/bno055/bno055_sl.c
@@ -0,0 +1,557 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Serial line interface for Bosh BNO055 IMU (via serdev).
+ * This file implements serial communication up to the register read/write
+ * level.
+ *
+ * Copyright (C) 2021 Istituto Italiano di Tecnologia
+ * Electronic Design Laboratory
+ * Written by Andrea Merello <andrea.merello@iit.it>
+ *
+ * This driver is besed on
+ * Plantower PMS7003 particulate matter sensor driver
+ * Which is
+ * Copyright (c) Tomasz Duszynski <tduszyns@gmail.com>
+ */
+
+#include <linux/completion.h>
+#include <linux/device.h>
+#include <linux/errno.h>
+#include <linux/jiffies.h>
+#include <linux/kernel.h>
+#include <linux/mod_devicetable.h>
+#include <linux/module.h>
+#include <linux/mutex.h>
+#include <linux/regmap.h>
+#include <linux/serdev.h>
+
+#include "bno055.h"
+
+/*
+ * Register writes cmd have the following format
+ * +------+------+-----+-----+----- ... ----+
+ * | 0xAA | 0xOO | REG | LEN | payload[LEN] |
+ * +------+------+-----+-----+----- ... ----+
+ *
+ * Register write responses have the following format
+ * +------+----------+
+ * | 0xEE | ERROCODE |
+ * +------+----------+
+ *
+ * .. except when writing the SYS_RST bit (i.e. triggering a system reset); in
+ * case the IMU accepts the command, then it resets without responding. We don't
+ * handle this (yet) here (so we inform the common bno055 code not to perform
+ * sw resets - bno055 on serial bus basically requires the hw reset pin).
+ *
+ * Register read have the following format
+ * +------+------+-----+-----+
+ * | 0xAA | 0xO1 | REG | LEN |
+ * +------+------+-----+-----+
+ *
+ * Successful register read response have the following format
+ * +------+-----+----- ... ----+
+ * | 0xBB | LEN | payload[LEN] |
+ * +------+-----+----- ... ----+
+ *
+ * Failed register read response have the following format
+ * +------+--------+
+ * | 0xEE | ERRCODE| (ERRCODE always > 1)
+ * +------+--------+
+ *
+ * Error codes are
+ * 01: OK
+ * 02: read/write FAIL
+ * 04: invalid address
+ * 05: write on RO
+ * 06: wrong start byte
+ * 07: bus overrun
+ * 08: len too high
+ * 09: len too low
+ * 10: bus RX byte timeout (timeout is 30mS)
+ *
+ *
+ * **WORKAROUND ALERT**
+ *
+ * Serial communication seems very fragile: the BNO055 buffer seems to overflow
+ * very easy; BNO055 seems able to sink few bytes, then it needs a brief pause.
+ * On the other hand, it is also picky on timeout: if there is a pause > 30mS in
+ * between two bytes then the transaction fails (IMU internal RX FSM resets).
+ *
+ * BNO055 has been seen also failing to process commands in case we send them
+ * too close each other (or if it is somehow busy?)
+ *
+ * In particular I saw these scenarios:
+ * 1) If we send 2 bytes per time, then the IMU never(?) overflows.
+ * 2) If we send 4 bytes per time (i.e. the full header), then the IMU could
+ * overflow, but it seem to sink all 4 bytes, then it returns error.
+ * 3) If we send more than 4 bytes, the IMU could overflow, and I saw it sending
+ * error after 4 bytes are sent; we have troubles in synchronizing again,
+ * because we are still sending data, and the IMU interprets it as the 1st
+ * byte of a new command.
+ *
+ * While we must avoid case 3, we could send 4 bytes per time and eventually
+ * retry in case of failure; this seemed convenient for reads (which requires
+ * TXing exactly 4 bytes), however it has been seen that, depending by the IMU
+ * settings (e.g. LPF), failures became less or more frequent; in certain IMU
+ * configurations they are very rare, but in certain others we keeps failing
+ * even after like 30 retries.
+ *
+ * So, we just split TXes in [2-bytes + delay] steps, and still keep an eye on
+ * the IMU response; in case it overflows (which is now unlikely), we retry.
+ */
+
+/*
+ * Read operation overhead:
+ * 4 bytes req + 2byte resp hdr.
+ * 6 bytes = 60 bit (considering 1start + 1stop bits).
+ * 60/115200 = ~520uS + about 2500mS dealay -> ~3mS
+ * In 3mS we could read back about 34 bytes that means 17 samples, this means
+ * that in case of scattered read in which the gap is 17 samples or less it is
+ * still convenient to go for a burst.
+ * We have to take into account also IMU response time - IMU seems to be often
+ * reasonably quick to respond, but sometimes it seems to be in some "critical
+ * section" in which it delays handling of serial protocol. Because of this we
+ * round-up to 22, which is the max number of samples, always bursting indeed.
+ */
+#define BNO055_SL_XFER_BURST_BREAK_THRESHOLD 22
+
+struct bno055_sl_priv {
+ struct serdev_device *serdev;
+ struct completion cmd_complete;
+ enum {
+ CMD_NONE,
+ CMD_READ,
+ CMD_WRITE,
+ } expect_response;
+ int expected_data_len;
+ u8 *response_buf;
+
+ /**
+ * enum cmd_status - represent the status of a command sent to the HW.
+ * @STATUS_OK: The command executed successfully.
+ * @STATUS_FAIL: The command failed: HW responded with an error.
+ * @STATUS_CRIT: The command failed: the serial communication failed.
+ */
+ enum {
+ STATUS_OK = 0,
+ STATUS_FAIL = 1,
+ STATUS_CRIT = -1
+ } cmd_status;
+ struct mutex lock;
+
+ /* Only accessed in RX callback context. No lock needed. */
+ struct {
+ enum {
+ RX_IDLE,
+ RX_START,
+ RX_DATA
+ } state;
+ int databuf_count;
+ int expected_len;
+ int type;
+ } rx;
+
+ /* Never accessed in behalf of RX callback context. No lock needed */
+ bool cmd_stale;
+};
+
+static int bno055_sl_send_chunk(struct bno055_sl_priv *priv, u8 *data, int len)
+{
+ int ret;
+
+ dev_dbg(&priv->serdev->dev, "send (len: %d): %*ph", len, len, data);
+ ret = serdev_device_write(priv->serdev, data, len,
+ msecs_to_jiffies(25));
+ if (ret < 0)
+ return ret;
+
+ if (ret < len)
+ return -EIO;
+
+ return 0;
+}
+
+/*
+ * Sends a read or write command.
+ * 'data' can be NULL (used in read case). 'len' parameter is always valid; in
+ * case 'data' is non-NULL then it must match 'data' size.
+ */
+static int bno055_sl_do_send_cmd(struct bno055_sl_priv *priv,
+ bool read, int addr, int len, u8 *data)
+{
+ u8 hdr[] = {0xAA, read, addr, len};
+ int chunk_len;
+ int i = 0;
+ int ret;
+
+ while (1) {
+ ret = bno055_sl_send_chunk(priv, hdr + i * 2, 2);
+ if (ret)
+ goto fail;
+
+ if (i++ == 1)
+ break;
+ usleep_range(2000, 3000);
+ }
+
+ if (read)
+ return 0;
+
+ while (len) {
+ chunk_len = min(len, 2);
+ usleep_range(2000, 3000);
+ ret = bno055_sl_send_chunk(priv, data, chunk_len);
+ if (ret)
+ goto fail;
+ data += chunk_len;
+ len -= chunk_len;
+ }
+
+ return 0;
+fail:
+ /* waiting more than 30mS should clear the BNO055 internal state */
+ usleep_range(40000, 50000);
+ return ret;
+}
+
+static int bno_sl_send_cmd(struct bno055_sl_priv *priv,
+ bool read, int addr, int len, u8 *data)
+{
+ const int retry_max = 5;
+ int retry = retry_max;
+ int ret = 0;
+
+ /*
+ * In case previous command was interrupted we still neet to wait it to
+ * complete before we can issue new commands
+ */
+ if (priv->cmd_stale) {
+ ret = wait_for_completion_interruptible_timeout(&priv->cmd_complete,
+ msecs_to_jiffies(100));
+ if (ret == -ERESTARTSYS)
+ return -ERESTARTSYS;
+
+ priv->cmd_stale = false;
+ /* if serial protocol broke, bail out */
+ if (priv->cmd_status == STATUS_CRIT)
+ return -EIO;
+ }
+
+ /*
+ * Try to convince the IMU to cooperate.. as explained in the comments
+ * at the top of this file, the IMU could also refuse the command (i.e.
+ * it is not ready yet); retry in this case.
+ */
+ while (retry--) {
+ mutex_lock(&priv->lock);
+ priv->expect_response = read ? CMD_READ : CMD_WRITE;
+ reinit_completion(&priv->cmd_complete);
+ mutex_unlock(&priv->lock);
+
+ if (retry != (retry_max - 1))
+ dev_dbg(&priv->serdev->dev, "cmd retry: %d",
+ retry_max - retry);
+ ret = bno055_sl_do_send_cmd(priv, read, addr, len, data);
+ if (ret)
+ continue;
+
+ ret = wait_for_completion_interruptible_timeout(&priv->cmd_complete,
+ msecs_to_jiffies(100));
+ if (ret == -ERESTARTSYS) {
+ priv->cmd_stale = true;
+ return -ERESTARTSYS;
+ } else if (!ret) {
+ return -ETIMEDOUT;
+ }
+
+ if (priv->cmd_status == STATUS_OK)
+ return 0;
+ else if (priv->cmd_status == STATUS_CRIT)
+ return -EIO;
+
+ /* loop in case priv->cmd_status == STATUS_FAIL */
+ }
+
+ if (ret < 0)
+ return ret;
+ if (priv->cmd_status == STATUS_FAIL)
+ return -EINVAL;
+ return 0;
+}
+
+static int bno055_sl_write_reg(void *context, const void *_data, size_t count)
+{
+ u8 *data = (u8 *)_data;
+ struct bno055_sl_priv *priv = context;
+
+ if (count < 2) {
+ dev_err(&priv->serdev->dev, "Invalid write count %zu", count);
+ return -EINVAL;
+ }
+
+ dev_dbg(&priv->serdev->dev, "wr reg 0x%x = 0x%x", data[0], data[1]);
+ return bno_sl_send_cmd(priv, 0, data[0], count - 1, data + 1);
+}
+
+static int bno055_sl_read_reg(void *context,
+ const void *reg, size_t reg_size,
+ void *val, size_t val_size)
+{
+ int ret;
+ int reg_addr;
+ struct bno055_sl_priv *priv = context;
+
+ if (val_size > 128) {
+ dev_err(&priv->serdev->dev, "Invalid read valsize %d",
+ val_size);
+ return -EINVAL;
+ }
+
+ reg_addr = ((u8 *)reg)[0];
+ dev_dbg(&priv->serdev->dev, "rd reg 0x%x (len %d)", reg_addr, val_size);
+ mutex_lock(&priv->lock);
+ priv->expected_data_len = val_size;
+ priv->response_buf = val;
+ mutex_unlock(&priv->lock);
+
+ ret = bno_sl_send_cmd(priv, 1, reg_addr, val_size, NULL);
+
+ mutex_lock(&priv->lock);
+ priv->response_buf = NULL;
+ mutex_unlock(&priv->lock);
+
+ return ret;
+}
+
+/*
+ * Handler for received data; this is called from the reicever callback whenever
+ * it got some packet from the serial bus. The status tell us whether the
+ * packet is valid (i.e. header ok && received payload len consistent wrt the
+ * header). It's now our responsability to check whether this is what we
+ * expected, of whether we got some unexpected, yet valid, packet.
+ */
+static void bno055_sl_handle_rx(struct bno055_sl_priv *priv, int status)
+{
+ mutex_lock(&priv->lock);
+ switch (priv->expect_response) {
+ case CMD_NONE:
+ dev_warn(&priv->serdev->dev, "received unexpected, yet valid, data from sensor");
+ mutex_unlock(&priv->lock);
+ return;
+
+ case CMD_READ:
+ priv->cmd_status = status;
+ if (status == STATUS_OK &&
+ priv->rx.databuf_count != priv->expected_data_len) {
+ /*
+ * If we got here, then the lower layer serial protocol
+ * seems consistent with itself; if we got an unexpected
+ * amount of data then signal it as a non critical error
+ */
+ priv->cmd_status = STATUS_FAIL;
+ dev_warn(&priv->serdev->dev, "received an unexpected amount of, yet valid, data from sensor");
+ }
+ break;
+
+ case CMD_WRITE:
+ priv->cmd_status = status;
+ break;
+ }
+
+ priv->expect_response = CMD_NONE;
+ complete(&priv->cmd_complete);
+ mutex_unlock(&priv->lock);
+}
+
+/*
+ * Serdev receiver FSM. This tracks the serial communication and parse the
+ * header. It pushes packets to bno055_sl_handle_rx(), eventually communicating
+ * failures (i.e. malformed packets).
+ * Ideally it doesn't know anything about upper layer (i.e. if this is the
+ * packet we were really expecting), but since we copies the payload into the
+ * receiver buffer (that is not valid when i.e. we don't expect data), we
+ * snoop a bit in the upper layer..
+ * Also, we assume to RX one pkt per time (i.e. the HW doesn't send anything
+ * unless we require to AND we don't queue more than one request per time).
+ */
+static int bno055_sl_receive_buf(struct serdev_device *serdev,
+ const unsigned char *buf, size_t size)
+{
+ int status;
+ struct bno055_sl_priv *priv = serdev_device_get_drvdata(serdev);
+ int remaining = size;
+
+ if (size == 0)
+ return 0;
+
+ dev_dbg(&priv->serdev->dev, "recv (len %zu): %*ph ", size, size, buf);
+ switch (priv->rx.state) {
+ case RX_IDLE:
+ /*
+ * New packet.
+ * Check for its 1st byte, that identifies the pkt type.
+ */
+ if (buf[0] != 0xEE && buf[0] != 0xBB) {
+ dev_err(&priv->serdev->dev,
+ "Invalid packet start %x", buf[0]);
+ bno055_sl_handle_rx(priv, STATUS_CRIT);
+ break;
+ }
+ priv->rx.type = buf[0];
+ priv->rx.state = RX_START;
+ remaining--;
+ buf++;
+ priv->rx.databuf_count = 0;
+ fallthrough;
+
+ case RX_START:
+ /*
+ * Packet RX in progress, we expect either 1-byte len or 1-byte
+ * status depending by the packet type.
+ */
+ if (remaining == 0)
+ break;
+
+ if (priv->rx.type == 0xEE) {
+ if (remaining > 1) {
+ dev_err(&priv->serdev->dev, "EE pkt. Extra data received");
+ status = STATUS_CRIT;
+
+ } else {
+ status = (buf[0] == 1) ? STATUS_OK : STATUS_FAIL;
+ }
+ bno055_sl_handle_rx(priv, status);
+ priv->rx.state = RX_IDLE;
+ break;
+
+ } else {
+ /*priv->rx.type == 0xBB */
+ priv->rx.state = RX_DATA;
+ priv->rx.expected_len = buf[0];
+ remaining--;
+ buf++;
+ }
+ fallthrough;
+
+ case RX_DATA:
+ /* Header parsed; now receiving packet data payload */
+ if (remaining == 0)
+ break;
+
+ if (priv->rx.databuf_count + remaining > priv->rx.expected_len) {
+ /*
+ * This is a inconsistency in serial protocol, we lost
+ * sync and we don't know how to handle further data
+ */
+ dev_err(&priv->serdev->dev, "BB pkt. Extra data received");
+ bno055_sl_handle_rx(priv, STATUS_CRIT);
+ priv->rx.state = RX_IDLE;
+ break;
+ }
+
+ mutex_lock(&priv->lock);
+ /*
+ * NULL e.g. when read cmd is stale or when no read cmd is
+ * actually pending.
+ */
+ if (priv->response_buf &&
+ /*
+ * Snoop on the upper layer protocol stuff to make sure not
+ * to write to an invalid memory. Apart for this, let's the
+ * upper layer manage any inconsistency wrt expected data
+ * len (as long as the serial protocol is consistent wrt
+ * itself (i.e. response header is consistent with received
+ * response len.
+ */
+ (priv->rx.databuf_count + remaining <= priv->expected_data_len))
+ memcpy(priv->response_buf + priv->rx.databuf_count,
+ buf, remaining);
+ mutex_unlock(&priv->lock);
+
+ priv->rx.databuf_count += remaining;
+
+ /*
+ * Reached expected len advertised by the IMU for the current
+ * packet. Pass it to the upper layer (for us it is just valid).
+ */
+ if (priv->rx.databuf_count == priv->rx.expected_len) {
+ bno055_sl_handle_rx(priv, STATUS_OK);
+ priv->rx.state = RX_IDLE;
+ }
+ break;
+ }
+
+ return size;
+}
+
+static const struct serdev_device_ops bno055_sl_serdev_ops = {
+ .receive_buf = bno055_sl_receive_buf,
+ .write_wakeup = serdev_device_write_wakeup,
+};
+
+static struct regmap_bus bno055_sl_regmap_bus = {
+ .write = bno055_sl_write_reg,
+ .read = bno055_sl_read_reg,
+};
+
+static int bno055_sl_probe(struct serdev_device *serdev)
+{
+ struct bno055_sl_priv *priv;
+ struct regmap *regmap;
+ int ret;
+
+ priv = devm_kzalloc(&serdev->dev, sizeof(*priv), GFP_KERNEL);
+ if (!priv)
+ return -ENOMEM;
+
+ serdev_device_set_drvdata(serdev, priv);
+ priv->serdev = serdev;
+ mutex_init(&priv->lock);
+ init_completion(&priv->cmd_complete);
+
+ serdev_device_set_client_ops(serdev, &bno055_sl_serdev_ops);
+ ret = devm_serdev_device_open(&serdev->dev, serdev);
+ if (ret)
+ return ret;
+
+ if (serdev_device_set_baudrate(serdev, 115200) != 115200) {
+ dev_err(&serdev->dev, "Cannot set required baud rate");
+ return -EIO;
+ }
+
+ ret = serdev_device_set_parity(serdev, SERDEV_PARITY_NONE);
+ if (ret) {
+ dev_err(&serdev->dev, "Cannot set required parity setting");
+ return ret;
+ }
+ serdev_device_set_flow_control(serdev, false);
+
+ regmap = devm_regmap_init(&serdev->dev, &bno055_sl_regmap_bus,
+ priv, &bno055_regmap_config);
+ if (IS_ERR(regmap)) {
+ dev_err(&serdev->dev, "Unable to init register map");
+ return PTR_ERR(regmap);
+ }
+
+ return bno055_probe(&serdev->dev, regmap,
+ BNO055_SL_XFER_BURST_BREAK_THRESHOLD, false);
+}
+
+static const struct of_device_id bno055_sl_of_match[] = {
+ { .compatible = "bosch,bno055" },
+ { }
+};
+MODULE_DEVICE_TABLE(of, bno055_sl_of_match);
+
+static struct serdev_device_driver bno055_sl_driver = {
+ .driver = {
+ .name = "bno055-sl",
+ .of_match_table = bno055_sl_of_match,
+ },
+ .probe = bno055_sl_probe,
+};
+module_serdev_device_driver(bno055_sl_driver);
+
+MODULE_AUTHOR("Andrea Merello <andrea.merello@iit.it>");
+MODULE_DESCRIPTION("Bosch BNO055 serdev interface");
+MODULE_LICENSE("GPL v2");
--
2.17.1