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commit b08221c40febcbda9309dd70c61cf1b0ebb0e351 upstream. Recently we met a touchscreen problem on some Thinkpad machines, the touchscreen driver (i2c-hid) is not loaded and the touchscreen can't work. An i2c ACPI device with the name WACF2200 is defined in the BIOS, with the current rule in matching_id(), this device will be regarded as a PNP device since there is WACFXXX in the acpi_pnp_device_ids[] and this PNP device is attached to the acpi device as the 1st physical_node, this will make the i2c bus match fail when i2c bus calls acpi_companion_match() to match the acpi_id_table in the i2c-hid driver. WACF2200 is an i2c device instead of a PNP device, after adding the string length comparing, the matching_id() will return false when matching WACF2200 and WACFXXX, and it is reasonable to compare the string length when matching two IDs. Suggested-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com> Signed-off-by: Hui Wang <hui.wang@canonical.com> Cc: All applicable <stable@vger.kernel.org> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.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 Restructured Text 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.