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Mario Limonciello (AMD) 7d62beb102 HID: i2c-hid: Resolve touchpad issues on Dell systems during S4
Dell systems utilize an EC-based touchpad emulation when the ACPI
touchpad _DSM is not invoked. This emulation acts as a secondary
master on the I2C bus, designed for scenarios where the I2C touchpad
driver is absent, such as in BIOS menus. Typically, loading the
i2c-hid module triggers the _DSM at initialization, disabling the
EC-based emulation.

However, if the i2c-hid module is missing from the boot kernel
used for hibernation snapshot restoration, the _DSM remains
uncalled, resulting in dual masters on the I2C bus and
subsequent arbitration errors. This issue arises when i2c-hid
resides in the rootfs instead of the kernel or initramfs.

To address this, switch from using the SYSTEM_SLEEP_PM_OPS()
macro to dedicated callbacks, introducing a specific
callback for restoring the S4 image. This callback ensures
the _DSM is invoked.

Signed-off-by: Mario Limonciello (AMD) <superm1@kernel.org>
Signed-off-by: Benjamin Tissoires <bentiss@kernel.org>
History 2025-09-16 10:24:46 +02:00
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README

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.