TCA9539-Q1: This IO extension chip can provide driver reference source code?

The registers of these I/O expanders are very simple. Therefore, it would not make much sense to provide a reference driver because it would consist almost entirely of the code needed to interface with the I²C host hardware and the OS driver interface, which is very system dependent.

The Linux driver can be found at git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/gpio/gpio-pca953x.c.