[PATCH v2 7/9] iio: imu: adis: add support product ID check in adis_initial_startup

[Alexandru Ardelean <alexandru.ardelean@xxxxxxxxxx>]

Each driver/chip that wants to validate it's product id, can now
specify a 'prod_id_reg' and an expected 'prod_id' value.
The 'prod_id' value is intentionally left 0 (uninitialized). There aren't
(yet) any product IDs with value 0; this enforces that both 'prod_id_reg'
and 'prod_id' are specified.

At the very least, this routine validates that the SPI connection to the
ADIS chip[s] works well.

Signed-off-by: Alexandru Ardelean <alexandru.ardelean@xxxxxxxxxx>
---
 drivers/iio/imu/adis.c       | 23 ++++++++++++++++++++++-
 include/linux/iio/imu/adis.h |  5 +++++
 2 files changed, 27 insertions(+), 1 deletion(-)

diff --git a/drivers/iio/imu/adis.c b/drivers/iio/imu/adis.c
index 0bd6e32cf577..a8afd01de4f3 100644
--- a/drivers/iio/imu/adis.c
+++ b/drivers/iio/imu/adis.c
@@ -373,6 +373,10 @@ static int adis_self_test(struct adis *adis)
  * via GPIOLIB. If no pin is configured a SW reset will be performed.
  * The RST pin for the ADIS devices should be configured as ACTIVE_LOW.
  *
+ * After the self-test operation is performed, the function will also check
+ * that the product ID is as expected. This assumes that drivers providing
+ * 'prod_id_reg' will also provide the 'prod_id'.
+ *
  * Returns 0 if the device is operational, a negative error code otherwise.
  *
  * This function should be called early on in the device initialization sequence
@@ -382,6 +386,7 @@ int __adis_initial_startup(struct adis *adis)
 {
 	const struct adis_timeout *timeouts = adis->data->timeouts;
 	struct gpio_desc *gpio;
+	uint16_t prod_id;
 	int ret;
 
 	/* check if the device has rst pin low */
@@ -401,7 +406,23 @@ int __adis_initial_startup(struct adis *adis)
 			return ret;
 	}
 
-	return adis_self_test(adis);
+	ret = adis_self_test(adis);
+	if (ret)
+		return ret;
+
+	if (!adis->data->prod_id_reg)
+		return 0;
+
+	ret = adis_read_reg_16(adis, adis->data->prod_id_reg, &prod_id);
+	if (ret)
+		return ret;
+
+	if (prod_id != adis->data->prod_id)
+		dev_warn(&adis->spi->dev,
+			 "Device ID(%u) and product ID(%u) do not match.",
+			 adis->data->prod_id, prod_id);
+
+	return 0;
 }
 EXPORT_SYMBOL_GPL(__adis_initial_startup);
 
diff --git a/include/linux/iio/imu/adis.h b/include/linux/iio/imu/adis.h
index b7feca4e5f26..ac7cfd073804 100644
--- a/include/linux/iio/imu/adis.h
+++ b/include/linux/iio/imu/adis.h
@@ -41,6 +41,8 @@ struct adis_timeout {
  * @glob_cmd_reg: Register address of the GLOB_CMD register
  * @msc_ctrl_reg: Register address of the MSC_CTRL register
  * @diag_stat_reg: Register address of the DIAG_STAT register
+ * @prod_id_reg: Register address of the PROD_ID register
+ * @prod_id: Product ID code that should be expected when reading @prod_id_reg
  * @self_test_reg: Register address to request self test command
  * @status_error_msgs: Array of error messgaes
  * @status_error_mask:
@@ -54,6 +56,9 @@ struct adis_data {
 	unsigned int glob_cmd_reg;
 	unsigned int msc_ctrl_reg;
 	unsigned int diag_stat_reg;
+	unsigned int prod_id_reg;
+
+	unsigned int prod_id;
 
 	unsigned int self_test_mask;
 	unsigned int self_test_reg;
-- 
2.20.1