iio: proximity: vl53l0x-i2c: claim direct mode for raw readsgrafted

vl53l0x_read_raw() starts a single-shot ranging measurement and reads
back the result. Once the triggered buffer is enabled the sensor runs in
continuous mode and its data-ready interrupt is routed to the trigger,
so a concurrent in_distance_raw read disturbs the streaming setup and
never gets its completion, returning -ETIMEDOUT.

The original submission claimed direct mode here, but it was dropped
during review because the driver had no buffer support at the time [1].
Continuous (buffered) mode was later added without restoring the
claim [2], reintroducing the conflict.

Reject direct reads while buffered capture is active by claiming direct
mode around the measurement, as the vl53l1x sibling already does.

Fixes: 762186c6e7b1 ("iio: proximity: vl53l0x-i2c: Added continuous mode support")
Link: https://lore.kernel.org/linux-iio/20180911160300.GA9212@himanshu-Vostro-3559/ [1]
Link: https://lore.kernel.org/linux-iio/20240909101508.263085-3-abhashkumarjha123@gmail.com/ [2]
Signed-off-by: Donggeun Yoo <donggeunyoo.kernel@gmail.com>
Cc: stable@vger.kernel.org
Signed-off-by: Jonathan Cameron <jonathan.cameron@oss.qualcomm.com>

1 files changed, 127 insertions, 0 deletions

diff --git a/Documentation/driver-api/iio/buffers.rst b/Documentation/driver-api/iio/buffers.rst
new file mode 100644
index 000000000..8779022e3
--- /dev/null
+++ b/Documentation/driver-api/iio/buffers.rst
@@ -0,0 +1,127 @@
+=======
+Buffers
+=======
+
+* struct iio_buffer — general buffer structure
+* :c:func:`iio_validate_scan_mask_onehot` — Validates that exactly one channel
+  is selected
+* :c:func:`iio_buffer_get` — Grab a reference to the buffer
+* :c:func:`iio_buffer_put` — Release the reference to the buffer
+
+The Industrial I/O core offers a way for continuous data capture based on a
+trigger source. Multiple data channels can be read at once from
+:file:`/dev/iio:device{X}` character device node, thus reducing the CPU load.
+
+IIO buffer sysfs interface
+==========================
+An IIO buffer has an associated attributes directory under
+:file:`/sys/bus/iio/devices/iio:device{X}/buffer/*`. Here are some of the
+existing attributes:
+
+* :file:`length`, the total number of data samples (capacity) that can be
+  stored by the buffer.
+* :file:`enable`, activate buffer capture.
+
+IIO buffer setup
+================
+
+The meta information associated with a channel reading placed in a buffer is
+called a scan element. The important bits configuring scan elements are
+exposed to userspace applications via the
+:file:`/sys/bus/iio/devices/iio:device{X}/scan_elements/` directory. This
+directory contains attributes of the following form:
+
+* :file:`enable`, used for enabling a channel. If and only if its attribute
+  is non *zero*, then a triggered capture will contain data samples for this
+  channel.
+* :file:`index`, the scan_index of the channel.
+* :file:`type`, description of the scan element data storage within the buffer
+  and hence the form in which it is read from user space.
+  Format is [be|le]:[f|s|u]bits/storagebits[Xrepeat][>>shift] .
+
+  * *be* or *le*, specifies big or little endian.
+  * *f*, specifies if floating-point.
+  * *s* or *u*, specifies if signed (2's complement) or unsigned.
+  * *bits*, is the number of valid data bits.
+  * *storagebits*, is the number of bits (after padding) that it occupies in the
+    buffer.
+  * *repeat*, specifies the number of bits/storagebits repetitions. When the
+    repeat element is 0 or 1, then the repeat value is omitted.
+  * *shift*, if specified, is the shift that needs to be applied prior to
+    masking out unused bits.
+
+For example, a driver for a 3-axis accelerometer with 12 bit resolution where
+data is stored in two 8-bits registers as follows::
+
+        7   6   5   4   3   2   1   0
+      +---+---+---+---+---+---+---+---+
+      |D3 |D2 |D1 |D0 | X | X | X | X | (LOW byte, address 0x06)
+      +---+---+---+---+---+---+---+---+
+
+        7   6   5   4   3   2   1   0
+      +---+---+---+---+---+---+---+---+
+      |D11|D10|D9 |D8 |D7 |D6 |D5 |D4 | (HIGH byte, address 0x07)
+      +---+---+---+---+---+---+---+---+
+
+will have the following scan element type for each axis::
+
+      $ cat /sys/bus/iio/devices/iio:device0/scan_elements/in_accel_y_type
+      le:s12/16>>4
+
+A user space application will interpret data samples read from the buffer as
+two byte little endian signed data, that needs a 4 bits right shift before
+masking out the 12 valid bits of data.
+
+For implementing buffer support a driver should initialize the following
+fields in iio_chan_spec definition::
+
+   struct iio_chan_spec {
+   /* other members */
+           int scan_index
+           struct {
+                   char format;
+                   u8 realbits;
+                   u8 storagebits;
+                   u8 shift;
+                   u8 repeat;
+                   enum iio_endian endianness;
+                  } scan_type;
+          };
+
+The driver implementing the accelerometer described above will have the
+following channel definition::
+
+   struct iio_chan_spec accel_channels[] = {
+           {
+                   .type = IIO_ACCEL,
+		   .modified = 1,
+		   .channel2 = IIO_MOD_X,
+		   /* other stuff here */
+		   .scan_index = 0,
+		   .scan_type = {
+		           .format = IIO_SCAN_FORMAT_SIGNED_INT,
+			   .realbits = 12,
+			   .storagebits = 16,
+			   .shift = 4,
+			   .endianness = IIO_LE,
+		   },
+           }
+           /* similar for Y (with channel2 = IIO_MOD_Y, scan_index = 1)
+            * and Z (with channel2 = IIO_MOD_Z, scan_index = 2) axis
+            */
+    }
+
+Here **scan_index** defines the order in which the enabled channels are placed
+inside the buffer. Channels with a lower **scan_index** will be placed before
+channels with a higher index. Each channel needs to have a unique
+**scan_index**.
+
+Setting **scan_index** to -1 can be used to indicate that the specific channel
+does not support buffered capture. In this case no entries will be created for
+the channel in the scan_elements directory.
+
+More details
+============
+.. kernel-doc:: include/linux/iio/buffer.h
+.. kernel-doc:: drivers/iio/industrialio-buffer.c
+   :export: