[PATCH] iio: inv_mpu6050: Do burst reads using spi/i2c directly

[Crestez Dan Leonard]

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.cres...@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