Re: Wrongly bound Elantech touchpad on Lenovo Yoga Slim 7

[Hans de Goede]

Hi,

On 2/4/22 18:39, Benjamin Tissoires wrote:
> Hi,
> 
> [adding Dmitry, the maintainer of the input tree and Hans, a colleague of mine]
> 
> On Fri, Feb 4, 2022 at 5:57 PM Takashi Iwai <tiwai@xxxxxxx> wrote:
>>
>> Hi,
>>
>> we've got a bug report on openSUSE Bugzilla about the broken touchpad
>> on Lenovo Yoga Slim 7:
>>   https://bugzilla.opensuse.org/show_bug.cgi?id=1193064
>>
>> The touchpad is an Elantech one, connected over i2c, and there are two
>> drivers supporting it.  Unfortunately, the default one the system
>> binds, elan-i2c input driver, doesn't seem working properly, while
>> i2c-hid driver works.
> 
> Hans, we do have a similar bug on RHEL at
> https://bugzilla.redhat.com/show_bug.cgi?id=2029078 (sorry, private
> bug).
> 
> IIRC you worked on the discrimination between i2c-hid and elan_i2c (I
> might be completely wrong though).

Yes I did work on that, but then the other way around making sure
that the i2c-hid driver would not bind to some devices which need
the elan_i2c touch*pad* driver.

And indeed as Dmitry points out:

> I believe we need to do what Hans did for Elan Touch*screen* driver and
> avoid binding to the device if it has i2c-hid-specific _DMS in ACPI.
> I.e. we need to replicate elants_acpi_is_hid_device().
> 
> Even better would be to factor it out, maybe not into a shared module
> but simply shared header with static inline function that we could share
> between elan drivers and maybe others as well.

I did fix a similar problem for the touchscreen driver last year or so.

I agree with Dmitry that we should try to avoid DMI matching here;
and I also agree that having some header with a static inline
acpi_is_hid_device() device helper would be good.

I'm a bit worried about the acpi_is_hid_device() approach though,
there is a lot of copy and pasting going on when vendors create
ACPI tables and sometimes a "PNP0C50" CID is present combined
with a valid i2c-hid _DSM method even though the device is not
an i2c-hid device, also see the i2c_hid_acpi_blacklist[] in
drivers/hid/i2c-hid/i2c-hid-acpi.c .

It seems to me that the problem is that the Lenovo Yoga Slim 7
is using what seems to be a very generic "ELAN0000" ACPI hardware
id instead of one of the many more specific ones.

So we could limit the acpi_is_hid_device() check to just the
"ELAN0000" ACPI hardware id I guess?

So I see the following 2 options:

1. Add an unconditional acpi_is_hid_device() check to elan_probe()
   and watch out for any bug-reports that this is causing breakage
   elsehwere
2. Add an acpi_is_hid_device() check to elan_probe() for ACPI enumerated
   touchpads with a hardware-id of ELAN0000 only; and still
   watch out for any bug-reports that this is causing breakage
   elsehwere just to be sure

Regards,

Hans





>> I'm not sure what's the best fix for this, but below a quick
>> workaround using a deny list with DMI matching.
>> If this is OK, I can resubmit the patch for merging.
>>
>> Any comments appreciated.
>>
>>
>> thanks,
>>
>> Takashi
>>
>> -- 8< --
>> From: Takashi Iwai <tiwai@xxxxxxx>
>> Subject: [PATCH] Input: elan_i2c: Add deny list for Lenovo Yoga Slim 7
>>
>> The touchpad on Lenovo Yoga Slim 7 doesn't work well with elan-i2c but
>> rather better with i2c-hid.  Add a deny list for avoiding to bind with
>> elan-i2c.
>>
>> BugLink: https://bugzilla.opensuse.org/show_bug.cgi?id=1193064
>> Signed-off-by: Takashi Iwai <tiwai@xxxxxxx>
>> ---
>>  drivers/input/mouse/elan_i2c_core.c | 19 +++++++++++++++++++
>>  1 file changed, 19 insertions(+)
>>
>> diff --git a/drivers/input/mouse/elan_i2c_core.c b/drivers/input/mouse/elan_i2c_core.c
>> index 47af62c12267..fd08481f7aea 100644
>> --- a/drivers/input/mouse/elan_i2c_core.c
>> +++ b/drivers/input/mouse/elan_i2c_core.c
>> @@ -18,6 +18,7 @@
>>  #include <linux/acpi.h>
>>  #include <linux/delay.h>
>>  #include <linux/device.h>
>> +#include <linux/dmi.h>
>>  #include <linux/firmware.h>
>>  #include <linux/i2c.h>
>>  #include <linux/init.h>
>> @@ -1222,6 +1223,20 @@ static void elan_disable_regulator(void *_data)
>>         regulator_disable(data->vcc);
>>  }
>>
>> +static const struct dmi_system_id elan_i2c_denylist[] __initconst = {
>> +#if IS_ENABLED(CONFIG_I2C_HID_ACPI)
>> +       {
>> +               /* Lenovo Yoga Slim 7 is better supported by i2c-hid */
>> +               .matches = {
>> +                       DMI_MATCH(DMI_SYS_VENDOR, "LENOVO"),
>> +                       DMI_MATCH(DMI_PRODUCT_NAME, "82A3"),
>> +                       DMI_MATCH(DMI_PRODUCT_VERSION, "Yoga Slim 7 14ITL05"),
>> +               },
>> +       },
>> +#endif
>> +       { }
>> +};
>> +
>>  static int elan_probe(struct i2c_client *client,
>>                       const struct i2c_device_id *dev_id)
>>  {
>> @@ -1233,6 +1248,10 @@ static int elan_probe(struct i2c_client *client,
>>
>>         if (IS_ENABLED(CONFIG_MOUSE_ELAN_I2C_I2C) &&
>>             i2c_check_functionality(client->adapter, I2C_FUNC_I2C)) {
>> +               if (dmi_check_system(elan_i2c_denylist)) {
>> +                       dev_info(dev, "Hits deny list, skipping\n");
>> +                       return -ENODEV;
>> +               }
>>                 transport_ops = &elan_i2c_ops;
>>         } else if (IS_ENABLED(CONFIG_MOUSE_ELAN_I2C_SMBUS) &&
>>                    i2c_check_functionality(client->adapter,
>> --
>> 2.31.1
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