Ok, I just played around with this a bit... (never had used the module before).

It seems you can ignore the "uninitialized value" warning. It originates from accessing $this->{DATA}{DEVICE} in Device::ParallelPort::drv::linux::init(), where the hash entry DEVICE is undefined — which isn't too surprising, as it isn't being set anywhere in the entire code (and AFAICT you can't set it by passing some value to the constructor, or some such). And when you dig a bit into the XS code, you'll find that it should be a device name (string). OTOH, that name is only ever being used in an error message you'd see in case the device initialisation should fail...

Anyhow, to get rid of the "uninitialized value", you could add

sub init {
    my ($this, $str, @params) = @_;
    $this->{DATA}{DEVICE} = "lp0";   # <---
    $this->{DATA}{BASE} = linux_opendev($this->{DATA}{DEVICE});
    ...
[download]

to the init() routine in Device/ParallelPort/drv/linux.pm  (the base address of lp0 (i.e. 0x378) is hardcoded anyway).

Other than that, the module seems to work here (I am using the USB parallel port device), i.e. with the following test code

#!/usr/bin/perl -w

use Device::ParallelPort;

my $port = Device::ParallelPort->new('linux');

if($port){
    $port->set_data(chr(0));
    $port->set_control(chr(0));
    show("Data",    $port->get_data());
    show("Control", $port->get_control());
    show("Status",  $port->get_status());

    print  "set  bit 0 to 0\n";  $port->set_bit(0, 0);
    printf "read bit 0:   %d\n", $port->get_bit(0);
    print  "set  bit 0 to 1\n";  $port->set_bit(0, 1);
    printf "read bit 0:   %d\n", $port->get_bit(0);
    print  "set  bit 0 to 0\n";  $port->set_bit(0, 0);
    printf "read bit 0:   %d\n", $port->get_bit(0);
    print  "set  bit 2 to 1\n";  $port->set_bit(2, 1);
    printf "read bit 2:   %d\n", $port->get_bit(2);

    show("Data",    $port->get_data());

    print "set data      'a' (0x61 01100001)\n";
    $port->set_data('a');
    show("Data",    $port->get_data());
    
    print "set control    4  (bit 2)\n";
    $port->set_control(chr(4));
    show("Control", $port->get_control());

    show("Status",  $port->get_status());
    
} else {
    die "Errore sul driver\n";
}

sub show {
    my $portname = shift;
    my $val  = ord shift;
    printf "%-13s %02x  %08b\n", "$portname port:", $val, $val;
}
[download]

I do get

Data port:    00  00000000
Control port: c0  11000000
Status port:  7f  01111111
set  bit 0 to 0
read bit 0:   0
set  bit 0 to 1
read bit 0:   1
set  bit 0 to 0
read bit 0:   0
set  bit 2 to 1
read bit 2:   1
Data port:    04  00000100
set data      'a' (0x61 01100001)
Data port:    61  01100001
set control    4  (bit 2)
Control port: c4  11000100
Status port:  7f  01111111
[download]

which kinda makes sense... (the upper two bits of the control port apparently are static — at least with my hardware)

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