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usb5744 supports SMBus Configuration and it may be configured via the SMBus slave interface during the hub start-up configuration stage. To program it driver uses i2c-bus phandle (added in commit '02be19e914b8 dt-bindings: usb: Add support for Microchip usb5744 hub controller') to get i2c client device and then based on usb5744 compatible check calls usb5744 i2c default initialization sequence. Apart from the USB command attach, prevent the hub from suspend. when the USB Attach with SMBus (0xAA56) command is issued to the hub, the hub is getting enumerated and then it puts in a suspend mode. This causes the hub to NAK any SMBus access made by the SMBus Master during this period and not able to see the hub's slave address while running the "i2c probe" command. Prevent the MCU from putting the HUB in suspend mode through register write. The BYPASS_UDC_SUSPEND bit (Bit 3) of the RuntimeFlags2 register at address 0x411D controls this aspect of the hub. The BYPASS_UDC_SUSPEND bit in register 0x411Dh must be set to ensure that the MCU is always enabled and ready to respond to SMBus runtime commands. This register needs to be written before the USB attach command is issued. The byte sequence is as follows: Slave addr: 0x2d 00 00 05 00 01 41 1D 08 Slave addr: 0x2d 99 37 00 Slave addr: 0x2d AA 56 00 Also since usb5744 i2c initialization routine uses i2c SMBus APIs invoke these APIs only when i2c driver is enabled in the kernel configuration. Signed-off-by: Radhey Shyam Pandey <radhey.shyam.pandey@amd.com> Link: https://lore.kernel.org/r/1725732196-70975-3-git-send-email-radhey.shyam.pandey@amd.com Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.