[...]

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+static int i2c_hid_polling_thread(void *i2c_hid)
+{

-   struct i2c_hid *ihid = i2c_hid;
-   struct i2c_client *client = ihid->client;
-   unsigned int polling_interval_idle;
-
-   while (1) {
-       /*


-        * re-calculate polling_interval_idle


-        * so the module parameters polling_interval_idle_ms can be


-        * changed dynamically through sysfs as polling_interval_active_us


-        */


-       polling_interval_idle = polling_interval_idle_ms * 1000;


-       if (test_bit(I2C_HID_READ_PENDING, &ihid->flags))


-       	usleep_range(50000, 100000);


-
-       if (kthread_should_stop())


-       	break;


-
-       while (interrupt_line_active(client)) {

I realize it's quite unlikely, but can't this be a endless loop if data is coming
in at a high enough rate? Maybe the maximum number of iterations could be limited here?

If we find HID reports are constantly read and send to front-end
application like libinput, won't it help expose the problem of the I2C
HiD device?

quoted

I'm not sure I completely understand your point. The reason why I wrote what I wrote
is that this kthread could potentially could go on forever (since `kthread_should_stop()`
is not checked in the inner while loop) if the data is supplied at a high enough rate.
That's why I said, to avoid this problem, only allow a certain number of iterations
for the inner loop, to guarantee that the kthread can stop in any case.

I mean if "data is supplied at a high enough rate" does happen, this is
an abnormal case and indicates a bug. So we shouldn't cover it up. We
expect the user to report it to us.

quoted

I agree in principle, but if this abnormal case ever occurs, that'll prevent
this module from being unloaded since `kthread_stop()` will hang because the
thread is "stuck" in the inner loop, never checking `kthread_should_stop()`.
That's why I think it makes sense to only allow a certain number of operations
for the inner loop, and maybe show a warning if that's exceeded:

for (i = 0; i < max_iter && interrupt_line_active(...); i++) {
....
}

WARN_ON[CE](i == max_iter[, "data is coming in at an unreasonably high rate"]);

I now realize that WARN_ON[CE] is probably not the best fit here, `hid_warn()` is possibly better.

or something like this, where `max_iter` could possibly be some value dependent on
`polling_interval_active_us`, or even just a constant.
[...]

Regards,
Barnabás Pőcze