iio: adis: Move burst mode into adis_data

Add burst mode variables in the per device specific data structure. As
some drivers support multiple devices with different burst sizes it
makes sense this data to be in `adis_data`. While moving the variables,
there are two main differences:

1. The `en`variable is dropped. If a device supports burst mode, it will
just use it as it will has better performance for almost all real use
cases.
2. Replace `extra_len` by `burst_len`. Users should now explicitly
define the length of the burst buffer as it is typically constant. This
also allows to remove the following line from the library:

```
/* All but the timestamp channel */
burst_length = (indio_dev->num_channels - 1) * sizeof(u16);
```

The library should not assume that a timestamp channel is defined.
Moreover, most parts also include some diagnostic data, crc, etc.. in
the burst buffer that needed to be included in an `extra_len` variable
which is not that nice. On top of this, some devices already start to
have some 32bit size channels ...

This patch is also a move to completely drop the `struct adis_burst`
from the library.
Signed-off-by: Nuno Sá <nuno.sa@analog.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Link: https://lore.kernel.org/r/20200917155223.218500-2-nuno.sa@analog.com

drivers/iio/imu/adis_buffer.c

@@ -26,12 +26,10 @@ static int adis_update_scan_mode_burst(struct iio_dev *indio_dev,
 	unsigned int burst_length, burst_max_length;
 	u8 *tx;
 
-	/* All but the timestamp channel */
-	burst_length = (indio_dev->num_channels - 1) * sizeof(u16);
-	burst_length += adis->burst->extra_len + adis->burst_extra_len;
+	burst_length = adis->data->burst_len + adis->burst_extra_len;
 
-	if (adis->burst->burst_max_len)
-		burst_max_length = adis->burst->burst_max_len;
+	if (adis->data->burst_max_len)
+		burst_max_length = adis->data->burst_max_len;
 	else
 		burst_max_length = burst_length;
 
@@ -47,7 +45,7 @@ static int adis_update_scan_mode_burst(struct iio_dev *indio_dev,
 	}
 
 	tx = adis->buffer + burst_max_length;
-	tx[0] = ADIS_READ_REG(adis->burst->reg_cmd);
+	tx[0] = ADIS_READ_REG(adis->data->burst_reg_cmd);
 	tx[1] = 0;
 
 	adis->xfer[0].tx_buf = tx;
@@ -76,7 +74,7 @@ int adis_update_scan_mode(struct iio_dev *indio_dev,
 	kfree(adis->xfer);
 	kfree(adis->buffer);
 
-	if (adis->burst && adis->burst->en)
+	if (adis->data->burst_len)
 		return adis_update_scan_mode_burst(indio_dev, scan_mask);
 
 	scan_count = indio_dev->scan_bytes / 2;

include/linux/iio/imu/adis.h

@@ -51,6 +51,11 @@ struct adis_timeout {
  * @timeouts: Chip specific delays
  * @enable_irq: Hook for ADIS devices that have a special IRQ enable/disable
  * @has_paging: True if ADIS device has paged registers
+ * @burst_reg_cmd:	Register command that triggers burst
+ * @burst_len:		Burst size in the SPI RX buffer. If @burst_max_len is defined,
+ *			this should be the minimum size supported by the device.
+ * @burst_max_len:	Holds the maximum burst size when the device supports
+ *			more than one burst mode with different sizes
  */
 struct adis_data {
 	unsigned int read_delay;
@@ -75,6 +80,10 @@ struct adis_data {
 	int (*enable_irq)(struct adis *adis, bool enable);
 
 	bool has_paging;
+
+	unsigned int burst_reg_cmd;
+	unsigned int burst_len;
+	unsigned int burst_max_len;
 };
 
 /**