[Unstable] [PATCH 1/1] HID: i2c-hid: Ignore input report if there's no data present on Elan touchpanels

[Kai-Heng Feng]

BugLink: https://bugs.launchpad.net/bugs/1813733

While using Elan touchpads, the message floods:
[  136.138487] i2c_hid i2c-DELL08D6:00: i2c_hid_get_input: incomplete report (14/65535)

Though the message flood is annoying, the device it self works without
any issue. I suspect that the device in question takes too much time to
pull the IRQ back to high after I2C host has done reading its data.

Since the host receives all useful data, let's ignore the input report
when there's no data.

Signed-off-by: Kai-Heng Feng <kai.heng.feng at canonical.com>
Signed-off-by: Benjamin Tissoires <benjamin.tissoires at redhat.com>
(backported from commit 1475af255e18f35dc46f8a7acc18354c73d45149 git://git.kernel.org/pub/scm/linux/kernel/git/hid/hid.git for-5.1/i2c-hid)
Signed-off-by: Kai-Heng Feng <kai.heng.feng at canonical.com>
---
 drivers/hid/i2c-hid/i2c-hid-core.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/drivers/hid/i2c-hid/i2c-hid-core.c b/drivers/hid/i2c-hid/i2c-hid-core.c
index c5edfa966343..90164fed08d3 100644
--- a/drivers/hid/i2c-hid/i2c-hid-core.c
+++ b/drivers/hid/i2c-hid/i2c-hid-core.c
@@ -50,6 +50,7 @@
 #define I2C_HID_QUIRK_NO_IRQ_AFTER_RESET	BIT(1)
 #define I2C_HID_QUIRK_NO_RUNTIME_PM		BIT(2)
 #define I2C_HID_QUIRK_DELAY_AFTER_SLEEP		BIT(3)
+#define I2C_HID_QUIRK_BOGUS_IRQ			BIT(4)
 
 /* flags */
 #define I2C_HID_STARTED		0
@@ -181,6 +182,8 @@ static const struct i2c_hid_quirks {
 		I2C_HID_QUIRK_NO_RUNTIME_PM },
 	{ I2C_VENDOR_ID_GOODIX, I2C_DEVICE_ID_GOODIX_01F0,
 		I2C_HID_QUIRK_NO_RUNTIME_PM },
+	{ USB_VENDOR_ID_ELAN, HID_ANY_ID,
+		 I2C_HID_QUIRK_BOGUS_IRQ },
 	{ 0, 0 }
 };
 
@@ -505,6 +508,12 @@ static void i2c_hid_get_input(struct i2c_hid *ihid)
 		return;
 	}
 
+	if (ihid->quirks & I2C_HID_QUIRK_BOGUS_IRQ && ret_size == 0xffff) {
+		dev_warn_once(&ihid->client->dev, "%s: IRQ triggered but "
+			      "there's no data\n", __func__);
+		return;
+	}
+
 	if ((ret_size > size) || (ret_size < 2)) {
 		dev_err(&ihid->client->dev, "%s: incomplete report (%d/%d)\n",
 			__func__, size, ret_size);
-- 
2.17.1