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Subject[PATCH] iio: inv_mpu6050: Do burst reads using spi/i2c directly
Date
Using regmap_read_bulk is wrong because it assumes that a range of
registers is being read. In our case reading from the fifo register will return
multiple values but this is *not* auto-increment.

This currently works by accident.

Signed-off-by: Crestez Dan Leonard <leonard.crestez@intel.com>
---

There is a need to determine if the underlying device is I2C or SPI here and
the current solution is not terribly pretty. Perhaps the i2c_client/spi_device
should be stored in inv_mpu6050_state instead?

I ran into this issue while attempting to enable regmap caching but perhaps it
could also be exposed by unusual i2c adapter capabilities?

drivers/iio/imu/inv_mpu6050/inv_mpu_ring.c | 33 ++++++++++++++++++++++++++----
1 file changed, 29 insertions(+), 4 deletions(-)

diff --git a/drivers/iio/imu/inv_mpu6050/inv_mpu_ring.c b/drivers/iio/imu/inv_mpu6050/inv_mpu_ring.c
index d070062..8455af0 100644
--- a/drivers/iio/imu/inv_mpu6050/inv_mpu_ring.c
+++ b/drivers/iio/imu/inv_mpu6050/inv_mpu_ring.c
@@ -21,6 +21,7 @@
#include <linux/interrupt.h>
#include <linux/kfifo.h>
#include <linux/poll.h>
+#include <linux/spi/spi.h>
#include "inv_mpu_iio.h"

static void inv_clear_kfifo(struct inv_mpu6050_state *st)
@@ -128,6 +129,13 @@ irqreturn_t inv_mpu6050_read_fifo(int irq, void *p)
u16 fifo_count;
s64 timestamp;

+ struct device *regmap_dev = regmap_get_device(st->map);
+ struct i2c_client *i2c;
+ struct spi_device *spi = NULL;
+
+ i2c = i2c_verify_client(regmap_dev);
+ spi = i2c ? NULL: to_spi_device(regmap_dev);
+
mutex_lock(&indio_dev->mlock);
if (!(st->chip_config.accl_fifo_enable |
st->chip_config.gyro_fifo_enable))
@@ -160,10 +168,27 @@ irqreturn_t inv_mpu6050_read_fifo(int irq, void *p)
fifo_count / bytes_per_datum + INV_MPU6050_TIME_STAMP_TOR)
goto flush_fifo;
while (fifo_count >= bytes_per_datum) {
- result = regmap_bulk_read(st->map, st->reg->fifo_r_w,
- data, bytes_per_datum);
- if (result)
- goto flush_fifo;
+ /*
+ * We need to do a large burst read from a single register.
+ *
+ * regmap_read_bulk assumes that multiple registers are
+ * involved but in our case st->reg->fifo_r_w + 1 is something
+ * completely unrelated.
+ */
+ if (spi) {
+ u8 cmd = st->reg->fifo_r_w | 0x80;
+ result = spi_write_then_read(spi,
+ &cmd, 1,
+ data, bytes_per_datum);
+ if (result)
+ goto flush_fifo;
+ } else {
+ result = i2c_smbus_read_i2c_block_data(i2c,
+ st->reg->fifo_r_w,
+ bytes_per_datum, data);
+ if (result != bytes_per_datum)
+ goto flush_fifo;
+ }

result = kfifo_out(&st->timestamps, &timestamp, 1);
/* when there is no timestamp, put timestamp as 0 */
--
2.5.5
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