iio: imu: bmi270: Add spi driver for bmi270 imu

Implement SPI driver for the Bosch BMI270 6-axis IMU. Provide raw read
write access to acceleration and angle velocity measurements via the SPI
interface on the device.

Signed-off-by: Alex Lanzano <lanzano.alex@gmail.com>
Link: https://patch.msgid.link/20241002033628.681812-1-lanzano.alex@gmail.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/imu/bmi270/Kconfig

@@ -18,3 +18,15 @@ config BMI270_I2C
 
 	  This driver can also be built as a module. If so, the module will be
 	  called bmi270_i2c.
+
+config BMI270_SPI
+	tristate "Bosch BMI270 SPI driver"
+	depends on SPI
+	select BMI270
+	select REGMAP_SPI
+	help
+	  Enable support for the Bosch BMI270 6-Axis IMU connected to SPI
+	  interface.
+
+	  This driver can also be built as a module. If so, the module will be
+	  called bmi270_spi.

drivers/iio/imu/bmi270/Makefile

@@ -4,3 +4,4 @@
 #
 obj-$(CONFIG_BMI270) += bmi270_core.o
 obj-$(CONFIG_BMI270_I2C) += bmi270_i2c.o
+obj-$(CONFIG_BMI270_SPI) += bmi270_spi.o

drivers/iio/imu/bmi270/bmi270.h

@@ -4,6 +4,7 @@
 #define BMI270_H_
 
 #include <linux/regmap.h>
+#include <linux/iio/iio.h>
 
 struct device;
 struct bmi270_data {

drivers/iio/imu/bmi270/bmi270_core.c

@@ -66,12 +66,6 @@ enum bmi270_scan {
 	BMI270_SCAN_GYRO_Z,
 };
 
-const struct regmap_config bmi270_regmap_config = {
-	.reg_bits = 8,
-	.val_bits = 8,
-};
-EXPORT_SYMBOL_NS_GPL(bmi270_regmap_config, IIO_BMI270);
-
 static int bmi270_get_data(struct bmi270_data *bmi270_device,
 			   int chan_type, int axis, int *val)
 {

drivers/iio/imu/bmi270/bmi270_i2c.c

@@ -9,12 +9,17 @@
 
 #include "bmi270.h"
 
+static const struct regmap_config bmi270_i2c_regmap_config = {
+	.reg_bits = 8,
+	.val_bits = 8,
+};
+
 static int bmi270_i2c_probe(struct i2c_client *client)
 {
 	struct regmap *regmap;
 	struct device *dev = &client->dev;
 
-	regmap = devm_regmap_init_i2c(client, &bmi270_regmap_config);
+	regmap = devm_regmap_init_i2c(client, &bmi270_i2c_regmap_config);
 	if (IS_ERR(regmap))
 		return dev_err_probe(dev, PTR_ERR(regmap),
 				     "Failed to init i2c regmap");

drivers/iio/imu/bmi270/bmi270_spi.c

@@ -0,0 +1,85 @@
+// SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+
+#include <linux/iio/iio.h>
+#include <linux/mod_devicetable.h>
+#include <linux/module.h>
+#include <linux/regmap.h>
+#include <linux/spi/spi.h>
+
+#include "bmi270.h"
+
+/*
+ * The following two functions are taken from the BMI323 spi driver code.
+ * In section 6.4 of the BMI270 data it specifies that after a read
+ * operation the first data byte from the device is a dummy byte
+ */
+static int bmi270_regmap_spi_read(void *spi, const void *reg_buf,
+				  size_t reg_size, void *val_buf,
+				  size_t val_size)
+{
+	return spi_write_then_read(spi, reg_buf, reg_size, val_buf, val_size);
+}
+
+static int bmi270_regmap_spi_write(void *spi, const void *data,
+				   size_t count)
+{
+	u8 *data_buff = (u8 *)data;
+
+	/*
+	 * Remove the extra pad byte since its only needed for the read
+	 * operation
+	 */
+	data_buff[1] = data_buff[0];
+	return spi_write_then_read(spi, data_buff + 1, count - 1, NULL, 0);
+}
+
+static const struct regmap_bus bmi270_regmap_bus = {
+	.read = bmi270_regmap_spi_read,
+	.write = bmi270_regmap_spi_write,
+};
+
+static const struct regmap_config bmi270_spi_regmap_config = {
+	.reg_bits = 8,
+	.val_bits = 8,
+	.pad_bits = 8,
+	.read_flag_mask = BIT(7),
+};
+
+static int bmi270_spi_probe(struct spi_device *spi)
+{
+	struct regmap *regmap;
+	struct device *dev = &spi->dev;
+
+	regmap = devm_regmap_init(dev, &bmi270_regmap_bus, dev,
+				  &bmi270_spi_regmap_config);
+	if (IS_ERR(regmap))
+		return dev_err_probe(dev, PTR_ERR(regmap),
+				     "Failed to init i2c regmap");
+
+	return bmi270_core_probe(dev, regmap);
+}
+
+static const struct spi_device_id bmi270_spi_id[] = {
+	{ "bmi270" },
+	{ }
+};
+
+static const struct of_device_id bmi270_of_match[] = {
+	{ .compatible = "bosch,bmi270" },
+	{ }
+};
+
+static struct spi_driver bmi270_spi_driver = {
+	.driver = {
+		.name = "bmi270",
+		.of_match_table = bmi270_of_match,
+	},
+	.probe = bmi270_spi_probe,
+	.id_table = bmi270_spi_id,
+};
+module_spi_driver(bmi270_spi_driver);
+
+MODULE_AUTHOR("Alex Lanzano");
+MODULE_DESCRIPTION("BMI270 driver");
+MODULE_LICENSE("GPL");
+MODULE_IMPORT_NS(IIO_BMI270);