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, 251 insertions, 0 deletions

diff --git a/Documentation/filesystems/afs.rst b/Documentation/filesystems/afs.rst
new file mode 100644
index 000000000..f15ba388b
--- /dev/null
+++ b/Documentation/filesystems/afs.rst
@@ -0,0 +1,251 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+====================
+kAFS: AFS FILESYSTEM
+====================
+
+.. Contents:
+
+ - Overview.
+ - Usage.
+ - Mountpoints.
+ - Dynamic root.
+ - Proc filesystem.
+ - The cell database.
+ - Security.
+ - The @sys substitution.
+
+
+Overview
+========
+
+This filesystem provides a fairly simple secure AFS filesystem driver. It is
+under development and does not yet provide the full feature set.  The features
+it does support include:
+
+ (*) Security (currently only AFS kaserver and KerberosIV tickets).
+
+ (*) File reading and writing.
+
+ (*) Automounting.
+
+ (*) Local caching (via fscache).
+
+It does not yet support the following AFS features:
+
+ (*) pioctl() system call.
+
+
+Compilation
+===========
+
+The filesystem should be enabled by turning on the kernel configuration
+options::
+
+	CONFIG_AF_RXRPC		- The RxRPC protocol transport
+	CONFIG_RXKAD		- The RxRPC Kerberos security handler
+	CONFIG_AFS_FS		- The AFS filesystem
+
+Additionally, the following can be turned on to aid debugging::
+
+	CONFIG_AF_RXRPC_DEBUG	- Permit AF_RXRPC debugging to be enabled
+	CONFIG_AFS_DEBUG	- Permit AFS debugging to be enabled
+
+They permit the debugging messages to be turned on dynamically by manipulating
+the masks in the following files::
+
+	/sys/module/af_rxrpc/parameters/debug
+	/sys/module/kafs/parameters/debug
+
+
+Usage
+=====
+
+When inserting the driver modules the root cell must be specified along with a
+list of volume location server IP addresses::
+
+	modprobe rxrpc
+	modprobe kafs rootcell=cambridge.redhat.com:172.16.18.73:172.16.18.91
+
+The first module is the AF_RXRPC network protocol driver.  This provides the
+RxRPC remote operation protocol and may also be accessed from userspace.  See:
+
+	Documentation/networking/rxrpc.rst
+
+The second module is the kerberos RxRPC security driver, and the third module
+is the actual filesystem driver for the AFS filesystem.
+
+Once the module has been loaded, more modules can be added by the following
+procedure::
+
+	echo add grand.central.org 18.9.48.14:128.2.203.61:130.237.48.87 >/proc/fs/afs/cells
+
+Where the parameters to the "add" command are the name of a cell and a list of
+volume location servers within that cell, with the latter separated by colons.
+
+Filesystems can be mounted anywhere by commands similar to the following::
+
+	mount -t afs "%cambridge.redhat.com:root.afs." /afs
+	mount -t afs "#cambridge.redhat.com:root.cell." /afs/cambridge
+	mount -t afs "#root.afs." /afs
+	mount -t afs "#root.cell." /afs/cambridge
+
+Where the initial character is either a hash or a percent symbol depending on
+whether you definitely want a R/W volume (percent) or whether you'd prefer a
+R/O volume, but are willing to use a R/W volume instead (hash).
+
+The name of the volume can be suffixes with ".backup" or ".readonly" to
+specify connection to only volumes of those types.
+
+The name of the cell is optional, and if not given during a mount, then the
+named volume will be looked up in the cell specified during modprobe.
+
+Additional cells can be added through /proc (see later section).
+
+
+Mountpoints
+===========
+
+AFS has a concept of mountpoints. In AFS terms, these are specially formatted
+symbolic links (of the same form as the "device name" passed to mount).  kAFS
+presents these to the user as directories that have a follow-link capability
+(i.e.: symbolic link semantics).  If anyone attempts to access them, they will
+automatically cause the target volume to be mounted (if possible) on that site.
+
+Automatically mounted filesystems will be automatically unmounted approximately
+twenty minutes after they were last used.  Alternatively they can be unmounted
+directly with the umount() system call.
+
+Manually unmounting an AFS volume will cause any idle submounts upon it to be
+culled first.  If all are culled, then the requested volume will also be
+unmounted, otherwise error EBUSY will be returned.
+
+This can be used by the administrator to attempt to unmount the whole AFS tree
+mounted on /afs in one go by doing::
+
+	umount /afs
+
+
+Dynamic Root
+============
+
+A mount option is available to create a serverless mount that is only usable
+for dynamic lookup.  Creating such a mount can be done by, for example::
+
+	mount -t afs none /afs -o dyn
+
+This creates a mount that just has an empty directory at the root.  Attempting
+to look up a name in this directory will cause a mountpoint to be created that
+looks up a cell of the same name, for example::
+
+	ls /afs/grand.central.org/
+
+
+Proc Filesystem
+===============
+
+The AFS module creates a "/proc/fs/afs/" directory and populates it:
+
+  (*) A "cells" file that lists cells currently known to the afs module and
+      their usage counts::
+
+	[root@andromeda ~]# cat /proc/fs/afs/cells
+	USE NAME
+	  3 cambridge.redhat.com
+
+  (*) A directory per cell that contains files that list volume location
+      servers, volumes, and active servers known within that cell::
+
+	[root@andromeda ~]# cat /proc/fs/afs/cambridge.redhat.com/servers
+	USE ADDR            STATE
+	  4 172.16.18.91        0
+	[root@andromeda ~]# cat /proc/fs/afs/cambridge.redhat.com/vlservers
+	ADDRESS
+	172.16.18.91
+	[root@andromeda ~]# cat /proc/fs/afs/cambridge.redhat.com/volumes
+	USE STT VLID[0]  VLID[1]  VLID[2]  NAME
+	  1 Val 20000000 20000001 20000002 root.afs
+
+
+The Cell Database
+=================
+
+The filesystem maintains an internal database of all the cells it knows and the
+IP addresses of the volume location servers for those cells.  The cell to which
+the system belongs is added to the database when modprobe is performed by the
+"rootcell=" argument or, if compiled in, using a "kafs.rootcell=" argument on
+the kernel command line.
+
+Further cells can be added by commands similar to the following::
+
+	echo add CELLNAME VLADDR[:VLADDR][:VLADDR]... >/proc/fs/afs/cells
+	echo add grand.central.org 18.9.48.14:128.2.203.61:130.237.48.87 >/proc/fs/afs/cells
+
+No other cell database operations are available at this time.
+
+
+Security
+========
+
+Secure operations are initiated by acquiring a key using the klog program.  A
+very primitive klog program is available at:
+
+	https://people.redhat.com/~dhowells/rxrpc/klog.c
+
+This should be compiled by::
+
+	make klog LDLIBS="-lcrypto -lcrypt -lkrb4 -lkeyutils"
+
+And then run as::
+
+	./klog
+
+Assuming it's successful, this adds a key of type RxRPC, named for the service
+and cell, e.g.: "afs@<cellname>".  This can be viewed with the keyctl program or
+by cat'ing /proc/keys::
+
+	[root@andromeda ~]# keyctl show
+	Session Keyring
+	       -3 --alswrv      0     0  keyring: _ses.3268
+		2 --alswrv      0     0   \_ keyring: _uid.0
+	111416553 --als--v      0     0   \_ rxrpc: afs@CAMBRIDGE.REDHAT.COM
+
+Currently the username, realm, password and proposed ticket lifetime are
+compiled into the program.
+
+It is not required to acquire a key before using AFS facilities, but if one is
+not acquired then all operations will be governed by the anonymous user parts
+of the ACLs.
+
+If a key is acquired, then all AFS operations, including mounts and automounts,
+made by a possessor of that key will be secured with that key.
+
+If a file is opened with a particular key and then the file descriptor is
+passed to a process that doesn't have that key (perhaps over an AF_UNIX
+socket), then the operations on the file will be made with key that was used to
+open the file.
+
+
+The @sys Substitution
+=====================
+
+The list of up to 16 @sys substitutions for the current network namespace can
+be configured by writing a list to /proc/fs/afs/sysname::
+
+	[root@andromeda ~]# echo foo amd64_linux_26 >/proc/fs/afs/sysname
+
+or cleared entirely by writing an empty list::
+
+	[root@andromeda ~]# echo >/proc/fs/afs/sysname
+
+The current list for current network namespace can be retrieved by::
+
+	[root@andromeda ~]# cat /proc/fs/afs/sysname
+	foo
+	amd64_linux_26
+
+When @sys is being substituted for, each element of the list is tried in the
+order given.
+
+By default, the list will contain one item that conforms to the pattern
+"<arch>_linux_26", amd64 being the name for x86_64.