Linux NFC subsystemSince 2011 the Linux kernel provides a NFC subsystem for some NFC devices. The same device can be used by the Linux NFC subsystem and also my CCID driver. We then have a conflict!
The kernel driver will use the device before the CCID driver has a chance to use it. Loading the CCID driver in pcsc-lite will then fail with an error message: "
Can't claim interface"
Devices supported by linux NFC driversAccording to drivers/nfc/pn533.c
The ACS ACR122U reader is also in the (unsupported) list of readers for my CCID driver.
So if you have such a reader and a "recent" Linux kernel (version 3.5 or more) you may not be able to use the CCID driver with this device.
Work aroundSo the CCID driver can use the ACS ACR122U you need to first unload the pn533 kernel driver.
[update April 14th 2017]To remove the pn533 kernel module use:
$ sudo rmmod pn533
[update December 15th 2018]The Linux kernel driver is loaded each time you plug the device. So using rmmod to unload the kernel driver will work only once and you would have to do it again and again.
To permanently remove the pn533 kernel module use something like:
$ sudo rm -r /lib/modules/*/kernel/drivers/nfc/pn533