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, 97 insertions, 0 deletions

diff --git a/Documentation/virt/acrn/io-request.rst b/Documentation/virt/acrn/io-request.rst
new file mode 100644
index 000000000..6cc3ea0fa
--- /dev/null
+++ b/Documentation/virt/acrn/io-request.rst
@@ -0,0 +1,97 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+I/O request handling
+====================
+
+An I/O request of a User VM, which is constructed by the hypervisor, is
+distributed by the ACRN Hypervisor Service Module to an I/O client
+corresponding to the address range of the I/O request. Details of I/O request
+handling are described in the following sections.
+
+1. I/O request
+--------------
+
+For each User VM, there is a shared 4-KByte memory region used for I/O requests
+communication between the hypervisor and Service VM. An I/O request is a
+256-byte structure buffer, which is 'struct acrn_io_request', that is filled by
+an I/O handler of the hypervisor when a trapped I/O access happens in a User
+VM. ACRN userspace in the Service VM first allocates a 4-KByte page and passes
+the GPA (Guest Physical Address) of the buffer to the hypervisor. The buffer is
+used as an array of 16 I/O request slots with each I/O request slot being 256
+bytes. This array is indexed by vCPU ID.
+
+2. I/O clients
+--------------
+
+An I/O client is responsible for handling User VM I/O requests whose accessed
+GPA falls in a certain range. Multiple I/O clients can be associated with each
+User VM. There is a special client associated with each User VM, called the
+default client, that handles all I/O requests that do not fit into the range of
+any other clients. The ACRN userspace acts as the default client for each User
+VM.
+
+Below illustration shows the relationship between I/O requests shared buffer,
+I/O requests and I/O clients.
+
+::
+
+     +------------------------------------------------------+
+     |                                       Service VM     |
+     |+--------------------------------------------------+  |
+     ||      +----------------------------------------+  |  |
+     ||      | shared page            ACRN userspace  |  |  |
+     ||      |    +-----------------+  +------------+ |  |  |
+     ||   +----+->| acrn_io_request |<-+  default   | |  |  |
+     ||   |  | |  +-----------------+  | I/O client | |  |  |
+     ||   |  | |  |       ...       |  +------------+ |  |  |
+     ||   |  | |  +-----------------+                 |  |  |
+     ||   |  +-|--------------------------------------+  |  |
+     ||---|----|-----------------------------------------|  |
+     ||   |    |                             kernel      |  |
+     ||   |    |            +----------------------+     |  |
+     ||   |    |            | +-------------+  HSM |     |  |
+     ||   |    +--------------+             |      |     |  |
+     ||   |                 | | I/O clients |      |     |  |
+     ||   |                 | |             |      |     |  |
+     ||   |                 | +-------------+      |     |  |
+     ||   |                 +----------------------+     |  |
+     |+---|----------------------------------------------+  |
+     +----|-------------------------------------------------+
+          |
+     +----|-------------------------------------------------+
+     |  +-+-----------+                                     |
+     |  | I/O handler |              ACRN Hypervisor        |
+     |  +-------------+                                     |
+     +------------------------------------------------------+
+
+3. I/O request state transition
+-------------------------------
+
+The state transitions of an ACRN I/O request are as follows.
+
+::
+
+   FREE -> PENDING -> PROCESSING -> COMPLETE -> FREE -> ...
+
+- FREE: this I/O request slot is empty
+- PENDING: a valid I/O request is pending in this slot
+- PROCESSING: the I/O request is being processed
+- COMPLETE: the I/O request has been processed
+
+An I/O request in COMPLETE or FREE state is owned by the hypervisor. HSM and
+ACRN userspace are in charge of processing the others.
+
+4. Processing flow of I/O requests
+----------------------------------
+
+a. The I/O handler of the hypervisor will fill an I/O request with PENDING
+   state when a trapped I/O access happens in a User VM.
+b. The hypervisor makes an upcall, which is a notification interrupt, to
+   the Service VM.
+c. The upcall handler schedules a worker to dispatch I/O requests.
+d. The worker looks for the PENDING I/O requests, assigns them to different
+   registered clients based on the address of the I/O accesses, updates
+   their state to PROCESSING, and notifies the corresponding client to handle.
+e. The notified client handles the assigned I/O requests.
+f. The HSM updates I/O requests states to COMPLETE and notifies the hypervisor
+   of the completion via hypercalls.