[RFC 0/1] Input: elants_i2c - Do not bind to i2c-hid compatible ACPI instantiated devices

Hi All,

Here is a patch which should fix the touchscreen issues some people have
been seeing on some recent Lenovo AMD CPU using models:
https://bugzilla.kernel.org/show_bug.cgi?id=207759

There are 2 reasons why this is a RFC:

1. It is compile-tested only ATM, I'm waiting for feedback from the
reporters of the issue.

2. The fix which I wrote is somewhat simple. It should work, but there
might be older touchscreens which actually need to use the Elan specific
protocol implemented by elants_i2c.ko; while the ACPI-fwnode describing
the touchscreen falsely contains one of the i2c-hid ACPI compatiblity-id
strings. This would of course be a bug in the ACPI tables, but I have
seen this before.

2. might lead to regressions (or it might be a non-issue) so I was hoping
for some input on this from Benjamin as he originally wroter the elants_i2c
code.

Regards,

Hans



Hans de Goede (1):
  Input: elants_i2c - Do not bind to i2c-hid compatible ACPI
    instantiated devices

 drivers/input/touchscreen/elants_i2c.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

-- 
2.30.1

Several users have been reporting that elants_i2c gives several errors
during probe and that their touchscreen does not work on their Lenovo AMD
based laptops with a touchscreen with a ELAN0001 ACPI hardware-id:

[    0.550596] elants_i2c i2c-ELAN0001:00: i2c-ELAN0001:00 supply vcc33 not found, using dummy regulator
[    0.551836] elants_i2c i2c-ELAN0001:00: i2c-ELAN0001:00 supply vccio not found, using dummy regulator
[    0.560932] elants_i2c i2c-ELAN0001:00: elants_i2c_send failed (77 77 77 77): -121
[    0.562427] elants_i2c i2c-ELAN0001:00: software reset failed: -121
[    0.595925] elants_i2c i2c-ELAN0001:00: elants_i2c_send failed (77 77 77 77): -121
[    0.597974] elants_i2c i2c-ELAN0001:00: software reset failed: -121
[    0.621893] elants_i2c i2c-ELAN0001:00: elants_i2c_send failed (77 77 77 77): -121
[    0.622504] elants_i2c i2c-ELAN0001:00: software reset failed: -121
[    0.632650] elants_i2c i2c-ELAN0001:00: elants_i2c_send failed (4d 61 69 6e): -121
[    0.634256] elants_i2c i2c-ELAN0001:00: boot failed: -121
[    0.699212] elants_i2c i2c-ELAN0001:00: invalid 'hello' packet: 00 00 ff ff
[    1.630506] elants_i2c i2c-ELAN0001:00: Failed to read fw id: -121
[    1.645508] elants_i2c i2c-ELAN0001:00: unknown packet 00 00 ff ff

Despite these errors, the elants_i2c driver stays bound to the device
(it returns 0 from its probe method despite the errors), blocking the
i2c-hid driver from binding.

Manually unbinding the elants_i2c driver and binding the i2c-hid driver
makes the touchscreen work.

Add a check if the ACPI-fwnode for the touchscreen contains one of
the i2c-hid compatiblity-id strings, and if it does make elants_i2c
not bind, so that the i2c-hid driver can bind.

This assumes that non of the (older) elan touchscreens which actually
need the elants_i2c driver falsely advertise an i2c-hid compatiblity-id
string in their ACPI-fwnodes. If some of them actually do have this
false advertising, then this change may lead to regressions.

Note this change is a no-op for none ACPI instantiated i2c-clients
or when ACPI support is not enabled in the kernel.

Cc: Benjamin Tissoires <redacted>
BugLink: https://bugzilla.kernel.org/show_bug.cgi?id=207759
Signed-off-by: Hans de Goede <redacted>
---
 drivers/input/touchscreen/elants_i2c.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/drivers/input/touchscreen/elants_i2c.c b/drivers/input/touchscreen/elants_i2c.c
index d51cb910fba1..becb32397e6d 100644
--- a/drivers/input/touchscreen/elants_i2c.c
+++ b/drivers/input/touchscreen/elants_i2c.c

@@ -1228,6 +1228,12 @@ static void elants_i2c_power_off(void *_data)
 	}
 }
 
+static const struct acpi_device_id i2c_hid_ids[] = {
+	{"ACPI0C50", 0 },
+	{"PNP0C50", 0 },
+	{ },
+};
+
 static int elants_i2c_probe(struct i2c_client *client,
 			    const struct i2c_device_id *id)
 {

@@ -1236,6 +1242,10 @@ static int elants_i2c_probe(struct i2c_client *client,
 	unsigned long irqflags;
 	int error;
 
+	/* Don't bind to i2c-hid compatible devices, these are handled by the i2c-hid drv. */
+	if (acpi_match_device_ids(ACPI_COMPANION(&client->dev), i2c_hid_ids) == 0)
+		return -ENODEV;
+
 	if (!i2c_check_functionality(client->adapter, I2C_FUNC_I2C)) {
 		dev_err(&client->dev,
 			"%s: i2c check functionality error\n", DEVICE_NAME);

-- 
2.30.1