[V8,0/4] i2c: ls2x: Add support for the Loongson-2K/LS7A I2C controller

Hi all:

This patch series adds support for the I2C module found on various
Loongson systems with the Loongson-2K SoC or the Loongson LS7A bridge chip.

For now, the I2C driver is suitable for DT-based or ACPI-based systems.

I have tested on Loongson-3A5000LA+LS7A1000/LS7A2000, Loongson-2K1000LA
and Loongson-2K0500.

Thanks.

Changes since V7:
- patch (3/4)
  - I2C_LS2X should be added to the Kconfig/Makefile in Latin
    alphabetical order;
  - To avoid repeated type conversions, 'struct ls2x_i2c_priv *priv'
    replaces 'struct i2c_adapter *adap' as the function parameter,
    e.g. ls2x_i2c_start();
  - Refactor ls2x_i2c_stop() with readb_poll_timeout(), mainly with
    LS2X_SR_BUSY to indicate the status (success/timeout) of the stop
    command;
  - Remove extra parentheses;
  - For consistency, the variable 'r' in ls2x_i2c_probe() is renamed to
    'ret'.

Changes since V6:
- patch (1/4)
  - Add Reviewed-by tag.
- patch (3/4)
  - GPL-2.0 -> GPL-2.0-only;
  - Add property.h;
  - writew() should be used to operate I2C_LS2X_PRER, and drop the
    suffix of I2C_LS2X_PRER_LO/I2C_LS2X_PRER_HI;
  - Drop ls2x_i2c_priv->dev, for it can be completely replaced by
    'adapter.dev.parent';
  - Reasonable return value handling in ls2x_i2c_xfer_one();
  - Dropping the I2C_M_STOP flag judgment, the stop parameter of
    ls2x_i2c_xfer_one() represents the last msg;
  - Add comments for subsys_initcall();
  - Code formatting, such as dropping unnecessary blank lines.

Changes since V5:
- patch (1/4)
  - Add property.h.
- patch (3/4)
  - Put the ls2x_i2c_reginit() in front of irq requst;
  - Refact ls2x_i2c_adjust_bus_speed: discard the magic value of
    the divider register and LS2X_I2C_FREQ_STD is used to calculate
    the frequency;
  - Drop useless parameters: priv->suspended, and also disable I2C
    interrupts during suspend;
  - Drop ls2x_i2c_remove(), for the adapter will be auto deleted on
    driver detach;
  - Drop MODULE_ALIAS;
  - Code formatting, such as alignment.

Thanks Andy for your comments.

Changes since V4:
- patch (1/4)
  - Drop unneeded headers: of.h;
  - xxx_props -> xxx_properties.
- patch (2/4)
  - Add interrupt headers to fix syntax error found by Rob.
- patch (3/4)
  - Drop atmoic loop in ls2x_i2c_master_xfer(), I have tested it on the
    appropriate environment with no problems;
  - Define the corresponding bits in I2C_LS2X_CTR to avoid magic
    numbers;
  - dev_get_drvdata() is used to get ls2x_i2c_priv() in
    ls2x_i2c_suspend();
  - i2c_add_adapter() -> devm_i2c_add_adapter();
  - SET_SYSTEM_SLEEP_PM_OPS() -> DEFINE_RUNTIME_DEV_PM_OPS();
  - Code formatting, such as alignment.

    Details: https://lore.kernel.org/all/Y4e%2F6KewuHjAluSZ@smile.fi.intel.com/

Changes since V3:
- Addressed all review comments from v3
  - Change the changelog text to make it clearer (1/5);
  - Fix some minor bugs, such as formatting issues (2/5);
  - Fix some formatting issues (3/5);
  - Deep refactoring of code for clarity (4/5).
     Details: https://lore.kernel.org/all/Y4S2cnlAm3YYvZ8E@smile.fi.intel.com/

Thanks to all for their suggestions.

Changes since V2:
- Addressed all review comments from v2
  - Drop of_match_ptr() in i2c-gpio to avoid potential unused warnings
    (1/5);
  - Introduce i2c_gpio_get_props() function as the generic interface
    to get i2c-gpio props from DT or ACPI table (2/5);
  - Refact ls2x i2c code, similar to removing excessive goto tags (4/5).

Thanks to Andy and Mika for their suggestions.

Changes since V1:
- Remove the function of getting the static i2c bus number from ACPI "_UID";
- Fix build warning from kernel test robot.

Binbin Zhou (4):
  i2c: gpio: Add support on ACPI-based system
  dt-bindings: i2c: add Loongson LS2X I2C controller
  i2c: ls2x: Add driver for Loongson-2K/LS7A I2C controller
  LoongArch: Enable LS2X I2C in loongson3_defconfig

 .../bindings/i2c/loongson,ls2x-i2c.yaml       |  51 +++
 arch/loongarch/configs/loongson3_defconfig    |   1 +
 drivers/i2c/busses/Kconfig                    |  11 +
 drivers/i2c/busses/Makefile                   |   1 +
 drivers/i2c/busses/i2c-gpio.c                 |  28 +-
 drivers/i2c/busses/i2c-ls2x.c                 | 366 ++++++++++++++++++
 6 files changed, 448 insertions(+), 10 deletions(-)
 create mode 100644 Documentation/devicetree/bindings/i2c/loongson,ls2x-i2c.yaml
 create mode 100644 drivers/i2c/busses/i2c-ls2x.c