[BUG] gpiolib: cdev: can't read RELEASED event for last line

[Kent Gibson <warthog618@gmail.com>]

Hi Bart,

In testing I'm finding that I can't read the RELEASED event from the
chip fd when the last line on the chip is released.
The chip fd becomes readable, but when I try to read it I get ENODEV.

I suspect this change is the likely culprit:

533aae7c94db gpiolib: cdev: fix NULL-pointer dereferences

@@ -2425,6 +2449,9 @@ static ssize_t lineinfo_watch_read(struct file *file, char __user *buf,
        int ret;
        size_t event_size;

+       if (!cdev->gdev->chip)
+               return -ENODEV;
+

though I haven't bisected it yet to be sure.

Btw, that is testing on 6.4.0-rc3 mainline.

Cheers,
Kent.