[PATCH v4] i2c: acpi: Add DELL0A86 to i2c_acpi_force_100khz_device_ids

[YuXin Xiao <xiaoyueyoqwq@gmail.com>]

The ELAN 04F3:3185 touchpad exposed as DELL0A86 on the Dell Inspiron
13 5310 intermittently exhibits excessive smoothing when the I2C bus
runs at 400 kHz. During an affected period pointer movement becomes
severely sluggish and sticky for tens of seconds.

The ACPI firmware configures the touchpad bus for 400 kHz. Add DELL0A86
to i2c_acpi_force_100khz_device_ids so that the bus runs at 100 kHz, as
is already done for other touchpads exhibiting the same excessive
smoothing problem.

With the quirk applied, the kernel reports that the firmware requested
400 kHz and that the bus is forced to 100 kHz. The problem did not recur
during extended heavy use, including an S4 hibernate/resume cycle.

An independent 2021 report from another Dell Inspiron 13 5310 user
describes the same intermittent sticky behavior and identifies the same
DELL0A86 / 04F3:3185 touchpad.

Link: https://www.reddit.com/r/linuxquestions/comments/nsso5b/help_needed_with_sticky_touchpad_spoiling_brand/

Assisted-by: Codex:ChatGPT-5.6-Sol
Assisted-by: OpenCode:Ox Alpha (x-preview-f-free)

Acked-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Signed-off-by: YuXin Xiao <xiaoyueyoqwq@gmail.com>
---
Changes in v4:
- Add an independent public report for the same model, device, and symptom.
- No code changes.

 drivers/i2c/i2c-core-acpi.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/i2c/i2c-core-acpi.c b/drivers/i2c/i2c-core-acpi.c
index 8f3bdd5..3af0e05 100644
--- a/drivers/i2c/i2c-core-acpi.c
+++ b/drivers/i2c/i2c-core-acpi.c
@@ -371,6 +371,7 @@ static const struct acpi_device_id i2c_acpi_force_100khz_device_ids[] = {
 	 * the device works without issues on Windows at what is expected to be
 	 * a 400KHz frequency. The root cause of the issue is not known.
 	 */
+	{ "DELL0A86", 0 },
 	{ "DLL0945", 0 },
 	{ "ELAN0678", 0 },
 	{ "ELAN06FA", 0 },
-- 
2.53.0