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, 96 insertions, 0 deletions

diff --git a/Documentation/i2c/i2c-protocol.rst b/Documentation/i2c/i2c-protocol.rst
new file mode 100644
index 000000000..df0febfe6
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+++ b/Documentation/i2c/i2c-protocol.rst
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+================
+The I2C Protocol
+================
+
+This document is an overview of the basic I2C transactions and the kernel
+APIs to perform them.
+
+Key to symbols
+==============
+
+=============== =============================================================
+S               Start condition
+P               Stop condition
+Rd/Wr (1 bit)   Read/Write bit. Rd equals 1, Wr equals 0.
+A, NA (1 bit)   Acknowledge (ACK) and Not Acknowledge (NACK) bit
+Addr  (7 bits)  I2C 7 bit address. Note that this can be expanded to
+                get a 10 bit I2C address.
+Data  (8 bits)  A plain data byte.
+
+[..]            Data sent by I2C device, as opposed to data sent by the
+                host adapter.
+=============== =============================================================
+
+
+Simple send transaction
+=======================
+
+Implemented by i2c_master_send()::
+
+  S Addr Wr [A] Data [A] Data [A] ... [A] Data [A] P
+
+
+Simple receive transaction
+==========================
+
+Implemented by i2c_master_recv()::
+
+  S Addr Rd [A] [Data] A [Data] A ... A [Data] NA P
+
+
+Combined transactions
+=====================
+
+Implemented by i2c_transfer().
+
+They are just like the above transactions, but instead of a stop
+condition P a start condition S is sent and the transaction continues.
+An example of a byte read, followed by a byte write::
+
+  S Addr Rd [A] [Data] NA S Addr Wr [A] Data [A] P
+
+
+Modified transactions
+=====================
+
+The following modifications to the I2C protocol can also be generated by
+setting these flags for I2C messages. With the exception of I2C_M_NOSTART, they
+are usually only needed to work around device issues:
+
+I2C_M_IGNORE_NAK:
+    Normally message is interrupted immediately if there is [NA] from the
+    client. Setting this flag treats any [NA] as [A], and all of
+    message is sent.
+    These messages may still fail to SCL lo->hi timeout.
+
+I2C_M_NO_RD_ACK:
+    In a read message, master A/NA bit is skipped.
+
+I2C_M_NOSTART:
+    In a combined transaction, no 'S Addr Wr/Rd [A]' is generated at some
+    point. For example, setting I2C_M_NOSTART on the second partial message
+    generates something like::
+
+      S Addr Rd [A] [Data] NA Data [A] P
+
+    If you set the I2C_M_NOSTART variable for the first partial message,
+    we do not generate Addr, but we do generate the start condition S.
+    This will probably confuse all other clients on your bus, so don't
+    try this.
+
+    This is often used to gather transmits from multiple data buffers in
+    system memory into something that appears as a single transfer to the
+    I2C device but may also be used between direction changes by some
+    rare devices.
+
+I2C_M_REV_DIR_ADDR:
+    This toggles the Rd/Wr flag. That is, if you want to do a write, but
+    need to emit an Rd instead of a Wr, or vice versa, you set this
+    flag. For example::
+
+      S Addr Rd [A] Data [A] Data [A] ... [A] Data [A] P
+
+I2C_M_STOP:
+    Force a stop condition (P) after the message. Some I2C related protocols
+    like SCCB require that. Normally, you really don't want to get interrupted
+    between the messages of one transfer.