On Fri, Dec 11, 2020 at 1:43 AM Hui Wang <hui.wang@xxxxxxxxxxxxx> wrote:
>
> On 12/10/20 5:04 PM, Greg KH wrote:
> > On Thu, Dec 10, 2020 at 09:25:39AM +0800, Hui Wang 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;
> > Shouldn't you verify that the format is correct as well?
>
> I thought the rest code in this function will verify the format, just
> missing the length checking. But I was wrong, "a pnp device id has
> CCCdddd format" is not correct since WACFXXX is a valid id,
In fact, the "F" may be regarded as a hex digit and so this follows
the CCCdddd format too.
The problem with the current code is that it matches ACPI device IDs
in the WACFdddd format against the WACFXXX string, which is incorrect.
> I will follow Rafael's advice: compare two string's length.
Please do.
