Re: [RFCv3 2/6] i2c: add I2C Address Translator (ATR) support

[kernel test robot <lkp@intel.com>]

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Hi Luca,

[FYI, it's a private test report for your RFC patch.]
[auto build test WARNING on media-tree/master]
[also build test WARNING on wsa/i2c/for-next robh/for-next linux/master linus/master v5.17-rc2 next-20220204]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch]

url:    https://github.com/0day-ci/linux/commits/Luca-Ceresoli/i2c-core-let-adapters-be-notified-of-client-attach-detach/20220206-220012
base:   git://linuxtv.org/media_tree.git master
config: arc-allyesconfig (https://download.01.org/0day-ci/archive/20220207/202202070103.fFqVrrDP-lkp(a)intel.com/config)
compiler: arceb-elf-gcc (GCC) 11.2.0
reproduce (this is a W=1 build):
        wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
        chmod +x ~/bin/make.cross
        # https://github.com/0day-ci/linux/commit/9fb70b22e4017684d0c6e00e36fed5cf8dfcbde3
        git remote add linux-review https://github.com/0day-ci/linux
        git fetch --no-tags linux-review Luca-Ceresoli/i2c-core-let-adapters-be-notified-of-client-attach-detach/20220206-220012
        git checkout 9fb70b22e4017684d0c6e00e36fed5cf8dfcbde3
        # save the config file to linux build tree
        mkdir build_dir
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-11.2.0 make.cross O=build_dir ARCH=arc SHELL=/bin/bash drivers/i2c/ drivers/media/i2c/

If you fix the issue, kindly add following tag as appropriate
Reported-by: kernel test robot <lkp@intel.com>

All warnings (new ones prefixed by >>):

>> drivers/i2c/i2c-atr.c:3: warning: This comment starts with '/**', but isn't a kernel-doc comment. Refer Documentation/doc-guide/kernel-doc.rst
    * I2C Address Translator


vim +3 drivers/i2c/i2c-atr.c

   > 3	 * I2C Address Translator
     4	 *
     5	 * Copyright (c) 2019 Luca Ceresoli <luca@lucaceresoli.net>
     6	 *
     7	 * An I2C Address Translator (ATR) is a device with an I2C slave parent
     8	 * ("upstream") port and N I2C master child ("downstream") ports, and
     9	 * forwards transactions from upstream to the appropriate downstream port
    10	 * with a modified slave address. The address used on the parent bus is
    11	 * called the "alias" and is (potentially) different from the physical
    12	 * slave address of the child bus. Address translation is done by the
    13	 * hardware.
    14	 *
    15	 * An ATR looks similar to an i2c-mux except:
    16	 * - the address on the parent and child busses can be different
    17	 * - there is normally no need to select the child port; the alias used on
    18	 *   the parent bus implies it
    19	 *
    20	 * The ATR functionality can be provided by a chip with many other
    21	 * features. This file provides a helper to implement an ATR within your
    22	 * driver.
    23	 *
    24	 * The ATR creates a new I2C "child" adapter on each child bus. Adding
    25	 * devices on the child bus ends up in invoking the driver code to select
    26	 * an available alias. Maintaining an appropriate pool of available aliases
    27	 * and picking one for each new device is up to the driver implementer. The
    28	 * ATR maintains an table of currently assigned alias and uses it to modify
    29	 * all I2C transactions directed to devices on the child buses.
    30	 *
    31	 * A typical example follows.
    32	 *
    33	 * Topology:
    34	 *
    35	 *                       Slave X @ 0x10
    36	 *               .-----.   |
    37	 *   .-----.     |     |---+---- B
    38	 *   | CPU |--A--| ATR |
    39	 *   `-----'     |     |---+---- C
    40	 *               `-----'   |
    41	 *                       Slave Y @ 0x10
    42	 *
    43	 * Alias table:
    44	 *
    45	 *   Client  Alias
    46	 *   -------------
    47	 *      X    0x20
    48	 *      Y    0x30
    49	 *
    50	 * Transaction:
    51	 *
    52	 *  - Slave X driver sends a transaction (on adapter B), slave address 0x10
    53	 *  - ATR driver rewrites messages with address 0x20, forwards to adapter A
    54	 *  - Physical I2C transaction on bus A, slave address 0x20
    55	 *  - ATR chip propagates transaction on bus B with address translated to 0x10
    56	 *  - Slave X chip replies on bus B
    57	 *  - ATR chip forwards reply on bus A
    58	 *  - ATR driver rewrites messages with address 0x10
    59	 *  - Slave X driver gets back the msgs[], with reply and address 0x10
    60	 *
    61	 * Usage:
    62	 *
    63	 *  1. In your driver (typically in the probe function) add an ATR by
    64	 *     calling i2c_atr_new() passing your attach/detach callbacks
    65	 *  2. When the attach callback is called pick an appropriate alias,
    66	 *     configure it in your chip and return the chosen alias in the
    67	 *     alias_id parameter
    68	 *  3. When the detach callback is called, deconfigure the alias from
    69	 *     your chip and put it back in the pool for later usage
    70	 *
    71	 * Originally based on i2c-mux.c
    72	 */
    73	

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