On Thu, Dec 10, 2020 at 2:27 AM Hui Wang <hui.wang@xxxxxxxxxxxxx> wrote:
>
> 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 ACPI PNP matching rule, 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.
>
> An ACPI PNP device's id has fixed format and its string length equals
> 7, after adding this check in the matching_id, the touchscreen could
> work.
>
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Hui Wang <hui.wang@xxxxxxxxxxxxx>
> ---
> drivers/acpi/acpi_pnp.c | 4 ++++
> 1 file changed, 4 insertions(+)
>
> diff --git a/drivers/acpi/acpi_pnp.c b/drivers/acpi/acpi_pnp.c
> index 4ed755a963aa..5ce711b9b070 100644
> --- a/drivers/acpi/acpi_pnp.c
> +++ b/drivers/acpi/acpi_pnp.c
> @@ -319,6 +319,10 @@ static bool matching_id(const char *idstr, const char *list_id)
> {
> int i;
>
> + /* a pnp device id has CCCdddd format (C character, d digit), strlen should be 7 */
> + if (strlen(idstr) != 7)
> + return false;
What I meant was comparing the length of the arg strings and return
false if they don't match. Wouldn't that work?
> +
> if (memcmp(idstr, list_id, 3))
> return false;
>
> --
> 2.25.1
>
