iio: proximity: isl29501: Fix return type of isl29501_register_writegrafted

isl29501_register_write() was returning a u32 instead of an int.
Since the function returns negative error codes (such as -ERANGE or
return values from i2c_smbus_write_byte_data()), returning an unsigned
integer type prevents callers from correctly checking for negative error
conditions.

Fix this by changing the function return type from u32 to int.

This was found through manual code review.

Fixes: 1c28799257bc ("iio: light: isl29501: Add support for the ISL29501 ToF sensor.")
Signed-off-by: Salah Triki <salah.triki@gmail.com>
Reviewed-by: Joshua Crofts <joshua.crofts1@gmail.com>
Cc: stable@vger.kernel.org
Signed-off-by: Jonathan Cameron <jonathan.cameron@oss.qualcomm.com>

1 files changed, 610 insertions, 0 deletions

diff --git a/Documentation/admin-guide/blockdev/zram.rst b/Documentation/admin-guide/blockdev/zram.rst
new file mode 100644
index 000000000..148b7cf3b
--- /dev/null
+++ b/Documentation/admin-guide/blockdev/zram.rst
@@ -0,0 +1,610 @@
+========================================
+zram: Compressed RAM-based block devices
+========================================
+
+Introduction
+============
+
+The zram module creates RAM-based block devices named /dev/zram<id>
+(<id> = 0, 1, ...). Pages written to these disks are compressed and stored
+in memory itself. These disks allow very fast I/O and compression provides
+good amounts of memory savings. Some of the use cases include /tmp storage,
+use as swap disks, various caches under /var and maybe many more. :)
+
+Statistics for individual zram devices are exported through sysfs nodes at
+/sys/block/zram<id>/
+
+Usage
+=====
+
+There are several ways to configure and manage zram device(-s):
+
+a) using zram and zram_control sysfs attributes
+b) using zramctl utility, provided by util-linux (util-linux@vger.kernel.org).
+
+In this document we will describe only 'manual' zram configuration steps,
+IOW, zram and zram_control sysfs attributes.
+
+In order to get a better idea about zramctl please consult util-linux
+documentation, zramctl man-page or `zramctl --help`. Please be informed
+that zram maintainers do not develop/maintain util-linux or zramctl, should
+you have any questions please contact util-linux@vger.kernel.org
+
+Following shows a typical sequence of steps for using zram.
+
+WARNING
+=======
+
+For the sake of simplicity we skip error checking parts in most of the
+examples below. However, it is your sole responsibility to handle errors.
+
+zram sysfs attributes always return negative values in case of errors.
+The list of possible return codes:
+
+========  =============================================================
+-EBUSY	  an attempt to modify an attribute that cannot be changed once
+	  the device has been initialised. Please reset device first.
+-ENOMEM	  zram was not able to allocate enough memory to fulfil your
+	  needs.
+-EINVAL	  invalid input has been provided.
+-EAGAIN	  re-try operation later (e.g. when attempting to run recompress
+	  and writeback simultaneously).
+========  =============================================================
+
+If you use 'echo', the returned value is set by the 'echo' utility,
+and, in general case, something like::
+
+	echo foo > /sys/block/zram0/comp_algorithm
+	if [ $? -ne 0 ]; then
+		handle_error
+	fi
+
+should suffice.
+
+Load Module
+===========
+
+::
+
+	modprobe zram num_devices=4
+
+This creates 4 devices: /dev/zram{0,1,2,3}
+
+num_devices parameter is optional and tells zram how many devices should be
+pre-created. Default: 1.
+
+Select compression algorithm
+============================
+
+Using comp_algorithm device attribute one can see available and
+currently selected (shown in square brackets) compression algorithms,
+or change the selected compression algorithm (once the device is initialised
+there is no way to change compression algorithm).
+
+Examples::
+
+	#show supported compression algorithms
+	cat /sys/block/zram0/comp_algorithm
+	lzo [lz4]
+
+	#select lzo compression algorithm
+	echo lzo > /sys/block/zram0/comp_algorithm
+
+For the time being, the `comp_algorithm` content shows only compression
+algorithms that are supported by zram.
+
+Set compression algorithm parameters: Optional
+==============================================
+
+Compression algorithms may support specific parameters which can be
+tweaked for particular dataset. ZRAM has an `algorithm_params` device
+attribute which provides a per-algorithm params configuration.
+
+For example, several compression algorithms support `level` parameter.
+In addition, certain compression algorithms support pre-trained dictionaries,
+which significantly change algorithms' characteristics. In order to configure
+compression algorithm to use external pre-trained dictionary, pass full
+path to the `dict` along with other parameters::
+
+	#pass path to pre-trained zstd dictionary
+	echo "algo=zstd dict=/etc/dictionary" > /sys/block/zram0/algorithm_params
+
+	#pass path to pre-trained zstd dictionary and compression level
+	echo "algo=zstd level=8 dict=/etc/dictionary" > \
+		/sys/block/zram0/algorithm_params
+
+	#same, but using algorithm priority
+	echo "algo=zstd priority=1" > /sys/block/zram0/recomp_algorithm
+	echo "priority=1 dict=/etc/dictionary" > \
+		/sys/block/zram0/algorithm_params
+
+Each write to `algorithm_params` replaces the entire set of parameters of
+the corresponding algorithm, parameters that are not listed in the write
+are reset to their default values.  Configure all of the parameters of an
+algorithm in one write::
+
+	#WRONG: the second write resets level back to its default value
+	echo "algo=zstd level=8" > /sys/block/zram0/algorithm_params
+	echo "algo=zstd dict=/etc/dictionary" > /sys/block/zram0/algorithm_params
+
+	#RIGHT
+	echo "algo=zstd level=8 dict=/etc/dictionary" > \
+		/sys/block/zram0/algorithm_params
+
+Select the compression algorithm before configuring its parameters.  The
+parameters of one algorithm are not necessarily valid for another one, so
+changing the algorithm of a particular priority resets that priority's
+parameters::
+
+	#WRONG: comp_algorithm write resets the previously configured level
+	echo "level=8" > /sys/block/zram0/algorithm_params
+	echo zstd > /sys/block/zram0/comp_algorithm
+
+	#RIGHT
+	echo zstd > /sys/block/zram0/comp_algorithm
+	echo "algo=zstd level=8" > /sys/block/zram0/algorithm_params
+
+Parameters are algorithm specific: not all algorithms support pre-trained
+dictionaries, not all algorithms support `level`. Furthermore, for certain
+algorithms `level` controls the compression level (the higher the value the
+better the compression ratio, it even can take negatives values for some
+algorithms), for other algorithms `level` is acceleration level (the higher
+the value the lower the compression ratio).
+
+Parameters are handed over to the compression algorithm when the device is
+initialised, hence invalid parameters (or parameters that the selected
+algorithm does not support) are reported by the `disksize` write, and not
+by the `algorithm_params` write that has configured them.
+
+Set Disksize
+============
+
+Set disk size by writing the value to sysfs node 'disksize'.
+The value can be either in bytes or you can use mem suffixes.
+Examples::
+
+	# Initialize /dev/zram0 with 50MB disksize
+	echo $((50*1024*1024)) > /sys/block/zram0/disksize
+
+	# Using mem suffixes
+	echo 256K > /sys/block/zram0/disksize
+	echo 512M > /sys/block/zram0/disksize
+	echo 1G > /sys/block/zram0/disksize
+
+Note:
+There is little point creating a zram of greater than twice the size of memory
+since we expect a 2:1 compression ratio. Note that zram uses about 0.1% of the
+size of the disk when not in use so a huge zram is wasteful.
+
+Set memory limit: Optional
+==========================
+
+Set memory limit by writing the value to sysfs node 'mem_limit'.
+The value can be either in bytes or you can use mem suffixes.
+In addition, you could change the value in runtime.
+Examples::
+
+	# limit /dev/zram0 with 50MB memory
+	echo $((50*1024*1024)) > /sys/block/zram0/mem_limit
+
+	# Using mem suffixes
+	echo 256K > /sys/block/zram0/mem_limit
+	echo 512M > /sys/block/zram0/mem_limit
+	echo 1G > /sys/block/zram0/mem_limit
+
+	# To disable memory limit
+	echo 0 > /sys/block/zram0/mem_limit
+
+Activate
+========
+
+::
+
+	mkswap /dev/zram0
+	swapon /dev/zram0
+
+	mkfs.ext4 /dev/zram1
+	mount /dev/zram1 /tmp
+
+Add/remove zram devices
+=======================
+
+zram provides a control interface, which enables dynamic (on-demand) device
+addition and removal.
+
+In order to add a new /dev/zramX device, perform a read operation on the hot_add
+attribute. This will return either the new device's device id (meaning that you
+can use /dev/zram<id>) or an error code.
+
+Example::
+
+	cat /sys/class/zram-control/hot_add
+	1
+
+To remove the existing /dev/zramX device (where X is a device id)
+execute::
+
+	echo X > /sys/class/zram-control/hot_remove
+
+Stats
+=====
+
+Per-device statistics are exported as various nodes under /sys/block/zram<id>/
+
+A brief description of exported device attributes follows. For more details
+please read Documentation/ABI/testing/sysfs-block-zram.
+
+======================  ======  ===============================================
+Name            	access            description
+======================  ======  ===============================================
+disksize          	RW	show and set the device's disk size
+initstate         	RO	shows the initialization state of the device
+reset             	WO	trigger device reset
+mem_used_max      	WO	reset the `mem_used_max` counter (see later)
+mem_limit         	WO	specifies the maximum amount of memory ZRAM can
+				use to store the compressed data
+writeback_limit   	WO	specifies the maximum amount of write IO zram
+				can write out to backing device as 4KB unit
+writeback_limit_enable  RW	show and set writeback_limit feature
+writeback_batch_size	RW	show and set maximum number of in-flight
+				writeback operations
+compressed_writeback	RW	show and set compressed writeback feature
+comp_algorithm    	RW	show and change the compression algorithm
+algorithm_params	WO	setup compression algorithm parameters
+compact           	WO	trigger memory compaction
+debug_stat        	RO	this file is used for zram debugging purposes
+backing_dev	  	RW	set up backend storage for zram to write out
+idle		  	WO	mark allocated slot as idle
+======================  ======  ===============================================
+
+User space is advised to use the following files to read the device statistics.
+
+File /sys/block/zram<id>/stat
+
+Represents block layer statistics. Read Documentation/block/stat.rst for
+details.
+
+File /sys/block/zram<id>/io_stat
+
+The stat file represents device's I/O statistics not accounted by block
+layer and, thus, not available in zram<id>/stat file. It consists of a
+single line of text and contains the following stats separated by
+whitespace:
+
+ =============    =============================================================
+ failed_reads     The number of failed reads
+ failed_writes    The number of failed writes
+ invalid_io       The number of non-page-size-aligned I/O requests
+ notify_free      Depending on device usage scenario it may account
+
+                  a) the number of pages freed because of swap slot free
+                     notifications
+                  b) the number of pages freed because of
+                     REQ_OP_DISCARD requests sent by bio. The former ones are
+                     sent to a swap block device when a swap slot is freed,
+                     which implies that this disk is being used as a swap disk.
+
+                  The latter ones are sent by filesystem mounted with
+                  discard option, whenever some data blocks are getting
+                  discarded.
+ =============    =============================================================
+
+File /sys/block/zram<id>/mm_stat
+
+The mm_stat file represents the device's mm statistics. It consists of a single
+line of text and contains the following stats separated by whitespace:
+
+ ================ =============================================================
+ orig_data_size   uncompressed size of data stored in this disk.
+                  Unit: bytes
+ compr_data_size  compressed size of data stored in this disk
+ mem_used_total   the amount of memory allocated for this disk. This
+                  includes allocator fragmentation and metadata overhead,
+                  allocated for this disk. So, allocator space efficiency
+                  can be calculated using compr_data_size and this statistic.
+                  Unit: bytes
+ mem_limit        the maximum amount of memory ZRAM can use to store
+                  the compressed data
+ mem_used_max     the maximum amount of memory zram has consumed to
+                  store the data
+ same_pages       the number of same element filled pages written to this disk.
+                  No memory is allocated for such pages.
+ pages_compacted  the number of pages freed during compaction
+ huge_pages	  the number of incompressible pages
+ huge_pages_since the number of incompressible pages since zram set up
+ ================ =============================================================
+
+File /sys/block/zram<id>/bd_stat
+
+The bd_stat file represents a device's backing device statistics. It consists of
+a single line of text and contains the following stats separated by whitespace:
+
+ ============== =============================================================
+ bd_count	size of data written in backing device.
+		Unit: 4K bytes
+ bd_reads	the number of reads from backing device
+		Unit: 4K bytes
+ bd_writes	the number of writes to backing device
+		Unit: 4K bytes
+ ============== =============================================================
+
+Deactivate
+==========
+
+::
+
+	swapoff /dev/zram0
+	umount /dev/zram1
+
+Reset
+=====
+
+	Write any positive value to 'reset' sysfs node::
+
+		echo 1 > /sys/block/zram0/reset
+		echo 1 > /sys/block/zram1/reset
+
+	This frees all the memory allocated for the given device and
+	resets the disksize to zero. You must set the disksize again
+	before reusing the device.
+
+Optional Feature
+================
+
+IDLE pages tracking
+-------------------
+
+zram has built-in support for idle pages tracking (that is, allocated but
+not used pages). This feature is useful for e.g. zram writeback and
+recompression. In order to mark pages as idle, execute the following command::
+
+	echo all > /sys/block/zramX/idle
+
+This will mark all allocated zram pages as idle. The idle mark will be
+removed only when the page (block) is accessed (e.g. overwritten or freed).
+Additionally, when CONFIG_ZRAM_TRACK_ENTRY_ACTIME is enabled, pages can be
+marked as idle based on how many seconds have passed since the last access to
+a particular zram page::
+
+	echo 86400 > /sys/block/zramX/idle
+
+In this example, all pages which haven't been accessed in more than 86400
+seconds (one day) will be marked idle.
+
+writeback
+---------
+
+With CONFIG_ZRAM_WRITEBACK, zram can write idle/incompressible page
+to backing storage rather than keeping it in memory.
+To use the feature, admin should set up backing device via::
+
+	echo /dev/sda5 > /sys/block/zramX/backing_dev
+
+before disksize setting. It supports only partitions at this moment.
+If admin wants to use incompressible page writeback, they could do it via::
+
+	echo huge > /sys/block/zramX/writeback
+
+Admin can request writeback of idle pages at right timing via::
+
+	echo idle > /sys/block/zramX/writeback
+
+With the command, zram will writeback idle pages from memory to the storage.
+
+Additionally, if a user choose to writeback only huge and idle pages
+this can be accomplished with::
+
+        echo huge_idle > /sys/block/zramX/writeback
+
+If a user chooses to writeback only incompressible pages (pages that none of
+algorithms can compress) this can be accomplished with::
+
+	echo incompressible > /sys/block/zramX/writeback
+
+If an admin wants to write a specific page in zram device to the backing device,
+they could write a page index into the interface::
+
+	echo "page_index=1251" > /sys/block/zramX/writeback
+
+In Linux 6.16 this interface underwent some rework.  First, the interface
+now supports `key=value` format for all of its parameters (`type=huge_idle`,
+etc.)  Second, the support for `page_indexes` was introduced, which specify
+`LOW-HIGH` range (or ranges) of pages to be written-back.  This reduces the
+number of syscalls, but more importantly this enables optimal post-processing
+target selection strategy. Usage example::
+
+	echo "type=idle" > /sys/block/zramX/writeback
+	echo "page_indexes=1-100 page_indexes=200-300" > \
+		/sys/block/zramX/writeback
+
+We also now permit multiple page_index params per call and a mix of
+single pages and page ranges::
+
+	echo page_index=42 page_index=99 page_indexes=100-200 \
+		page_indexes=500-700 > /sys/block/zramX/writeback
+
+If there are lots of write IO with flash device, potentially, it has
+flash wearout problem so that admin needs to design write limitation
+to guarantee storage health for entire product life.
+
+To overcome the concern, zram supports "writeback_limit" feature.
+The "writeback_limit_enable"'s default value is 0 so that it doesn't limit
+any writeback. IOW, if admin wants to apply writeback budget, they should
+enable writeback_limit_enable via::
+
+	$ echo 1 > /sys/block/zramX/writeback_limit_enable
+
+Once writeback_limit_enable is set, zram doesn't allow any writeback
+until admin sets the budget via /sys/block/zramX/writeback_limit.
+
+(If admin doesn't enable writeback_limit_enable, writeback_limit's value
+assigned via /sys/block/zramX/writeback_limit is meaningless.)
+
+If admin wants to limit writeback as per-day 400M, they could do it
+like below::
+
+	$ MB_SHIFT=20
+	$ 4K_SHIFT=12
+	$ echo $((400<<MB_SHIFT>>4K_SHIFT)) > \
+		/sys/block/zram0/writeback_limit.
+	$ echo 1 > /sys/block/zram0/writeback_limit_enable
+
+If admins want to allow further write again once the budget is exhausted,
+they could do it like below::
+
+	$ echo $((400<<MB_SHIFT>>4K_SHIFT)) > \
+		/sys/block/zram0/writeback_limit
+
+If an admin wants to see the remaining writeback budget since last set::
+
+	$ cat /sys/block/zramX/writeback_limit
+
+If an admin wants to disable writeback limit, they could do::
+
+	$ echo 0 > /sys/block/zramX/writeback_limit_enable
+
+The writeback_limit count will reset whenever you reset zram (e.g.,
+system reboot, echo 1 > /sys/block/zramX/reset) so keeping how many of
+writeback happened until you reset the zram to allocate extra writeback
+budget in next setting is user's job.
+
+By default zram stores written back pages in decompressed (raw) form, which
+means that writeback operation involves decompression of the page before
+writing it to the backing device.  This behavior can be changed by enabling
+`compressed_writeback` feature, which causes zram to write compressed pages
+to the backing device, thus avoiding decompression overhead.  To enable
+this feature, execute::
+
+	$ echo yes > /sys/block/zramX/compressed_writeback
+
+Note that this feature should be configured before the `zramX` device is
+initialized.
+
+Depending on backing device storage type, writeback operation may benefit
+from a higher number of in-flight write requests (batched writes).  The
+number of maximum in-flight writeback operations can be configured via
+`writeback_batch_size` attribute.  To change the default value (which is 32),
+execute::
+
+	$ echo 64 > /sys/block/zramX/writeback_batch_size
+
+If admin wants to measure writeback count in a certain period, they could
+know it via /sys/block/zram0/bd_stat's 3rd column.
+
+recompression
+-------------
+
+With `CONFIG_ZRAM_MULTI_COMP`, zram can recompress pages using alternative
+(secondary) compression algorithms. The basic idea is that alternative
+compression algorithm can provide better compression ratio at a price of
+(potentially) slower compression/decompression speeds. Alternative compression
+algorithm can, for example, be more successful compressing huge pages (those
+that default algorithm failed to compress). Another application is idle pages
+recompression - pages that are cold and sit in the memory can be recompressed
+using more effective algorithm and, hence, reduce zsmalloc memory usage.
+
+With `CONFIG_ZRAM_MULTI_COMP`, zram supports up to 4 compression algorithms:
+one primary and up to 3 secondary ones. Primary zram compressor is explained
+in "3) Select compression algorithm", secondary algorithms are configured
+using recomp_algorithm device attribute.
+
+Example:::
+
+	#show supported recompression algorithms
+	cat /sys/block/zramX/recomp_algorithm
+	#1: lzo lzo-rle lz4 lz4hc [zstd]
+	#2: lzo lzo-rle lz4 [lz4hc] zstd
+
+Alternative compression algorithms are sorted by priority. In the example
+above, zstd is used as the first alternative algorithm, which has priority
+of 1, while lz4hc is configured as a compression algorithm with priority 2.
+Alternative compression algorithm's priority is provided during algorithms
+configuration:::
+
+	#select zstd recompression algorithm, priority 1
+	echo "algo=zstd priority=1" > /sys/block/zramX/recomp_algorithm
+
+	#select deflate recompression algorithm, priority 2
+	echo "algo=deflate priority=2" > /sys/block/zramX/recomp_algorithm
+
+Another device attribute that `CONFIG_ZRAM_MULTI_COMP` enables is `recompress`,
+which controls recompression.
+
+Examples:::
+
+	#IDLE pages recompression is activated by `idle` mode
+	echo "type=idle priority=1" > /sys/block/zramX/recompress
+
+	#HUGE pages recompression is activated by `huge` mode
+	echo "type=huge priority=2" > /sys/block/zram0/recompress
+
+	#HUGE_IDLE pages recompression is activated by `huge_idle` mode
+	echo "type=huge_idle priority=1" > /sys/block/zramX/recompress
+
+The number of idle pages can be significant, so user-space can pass a size
+threshold (in bytes) to the recompress knob: zram will recompress only pages
+of equal or greater size:::
+
+	#recompress all pages larger than 3000 bytes
+	echo "threshold=3000 priority=1" > /sys/block/zramX/recompress
+
+	#recompress idle pages larger than 2000 bytes
+	echo "type=idle threshold=2000 priority=1" > \
+		/sys/block/zramX/recompress
+
+It is also possible to limit the number of pages zram re-compression will
+attempt to recompress:::
+
+	echo "type=huge_idle priority=1 max_pages=42" > \
+		/sys/block/zramX/recompress
+
+It is advised to always specify `priority` parameter.  While it is also
+possible to specify `algo` parameter, so that `zram` will use algorithm's
+name to determine the priority, it is not recommended, since it can lead to
+unexpected results when the same algorithm is configured with different
+priorities (e.g. different parameters).  `priority` is the only way to
+guarantee that the expected algorithm will be used.
+
+memory tracking
+===============
+
+With CONFIG_ZRAM_MEMORY_TRACKING, user can know information of the
+zram block. It could be useful to catch cold or incompressible
+pages of the process with*pagemap.
+
+If you enable the feature, you could see block state via
+/sys/kernel/debug/zram/zram0/block_state". The output is as follows::
+
+	  300    75.033841 .wh...
+	  301    63.806904 s.....
+	  302    63.806919 ..hi..
+	  303    62.801919 ....r.
+	  304   146.781902 ..hi.n
+
+First column
+	zram's block index.
+Second column
+	access time since the system was booted
+Third column
+	state of the block:
+
+	s:
+		same page
+	w:
+		written page to backing store
+	h:
+		huge page
+	i:
+		idle page
+	r:
+		recompressed page (secondary compression algorithm)
+	n:
+		none (including secondary) of algorithms could compress it
+
+First line of above example says 300th block is accessed at 75.033841sec
+and the block's state is huge so it is written back to the backing
+storage. It's a debugging feature so anyone shouldn't rely on it to work
+properly.
+
+Nitin Gupta
+ngupta@vflare.org