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    Subject[PATCH 5.10 534/717] ACPI: PNP: compare the string length in the matching_id()
    Date
    From: Hui Wang <hui.wang@canonical.com>

    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>

    ---
    drivers/acpi/acpi_pnp.c | 3 +++
    1 file changed, 3 insertions(+)

    --- a/drivers/acpi/acpi_pnp.c
    +++ b/drivers/acpi/acpi_pnp.c
    @@ -319,6 +319,9 @@ static bool matching_id(const char *idst
    {
    int i;

    + if (strlen(idstr) != strlen(list_id))
    + return false;
    +
    if (memcmp(idstr, list_id, 3))
    return false;


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