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iio: st_sensors: read each channel individually 

The current buffer read code tries to optimize reads from the
sensor data registers by issuing a single read operation across
all the indata registers.

This doesn't work: when the LIS331DL accelerometer sensor is
configured to open drain, active low interrupt mode, this will
just clear the XDA (X-axis data available) bit in the STATUS_REG
register (0x27), while YDA, ZDA and even ZYXDA remain set to 1,
and the internal logic of the sensor holds the DRDY (INT1) line
asserted (the value of the status register is 0xee).

If we instead issue one read operation per enabled channel
(X, Y, Z) things start working and we can use open drain and
active low interrupts.

Note that a backported patch fixing this issue will be heading
via the fixes branch but changes in this file already in staging-next
will make that patch 'look' rather different.  The code in here
is the correct one when that clash hits.

Cc: Giuseppe Barba <giuseppe.barba@st.com>
Cc: Denis Ciocca <denis.ciocca@st.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>
This commit is contained in:
Linus Walleij 2016-03-24 14:18:04 +01:00 committed by Jonathan Cameron
parent 850c25c857
commit 6436db37b4
1 changed files with 16 additions and 53 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

67
drivers/iio/common/st_sensors/st_sensors_buffer.c
View File

@ -24,67 +24,30 @@
int st_sensors_get_buffer_element(struct iio_dev *indio_dev, u8 *buf)
{
u8 addr[3]; /* no ST sensor has more than 3 channels */
int i, n = 0, len;
int i, len;
int total = 0;
struct st_sensor_data *sdata = iio_priv(indio_dev);
unsigned int num_data_channels = sdata->num_data_channels;
unsigned int byte_for_channel =
indio_dev->channels[0].scan_type.storagebits >> 3;
for (i = 0; i < num_data_channels; i++) {
unsigned int bytes_to_read;
if (test_bit(i, indio_dev->active_scan_mask)) {
addr[n] = indio_dev->channels[i].address;
n++;
}
}
switch (n) {
case 1:
len = sdata->tf->read_multiple_byte(&sdata->tb, sdata->dev,
addr[0], byte_for_channel, buf, sdata->multiread_bit);
break;
case 2:
if ((addr[1] - addr[0]) == byte_for_channel) {
bytes_to_read = indio_dev->channels[i].scan_type.storagebits >> 3;
len = sdata->tf->read_multiple_byte(&sdata->tb,
sdata->dev, addr[0], byte_for_channel * n,
buf, sdata->multiread_bit);
} else {
u8 *rx_array;
rx_array = kmalloc(byte_for_channel * num_data_channels,
GFP_KERNEL);
if (!rx_array)
return -ENOMEM;
sdata->dev, indio_dev->channels[i].address,
bytes_to_read,
buf + total, sdata->multiread_bit);
len = sdata->tf->read_multiple_byte(&sdata->tb,
sdata->dev, addr[0],
byte_for_channel * num_data_channels,
rx_array, sdata->multiread_bit);
if (len < 0) {
kfree(rx_array);
return len;
}
for (i = 0; i < n * byte_for_channel; i++) {
if (i < n)
buf[i] = rx_array[i];
else
buf[i] = rx_array[n + i];
}
kfree(rx_array);
len = byte_for_channel * n;
}
break;
case 3:
len = sdata->tf->read_multiple_byte(&sdata->tb, sdata->dev,
addr[0], byte_for_channel * num_data_channels,
buf, sdata->multiread_bit);
break;
default:
return -EINVAL;
}
if (len != byte_for_channel * n)
if (len < bytes_to_read)
return -EIO;
return len;
/* Advance the buffer pointer */
total += len;
}
}
return total;
}
EXPORT_SYMBOL(st_sensors_get_buffer_element);