use Fcntl qw/:flock/;
...
my $i2c = HiPi::Device::I2C->new(...);
...
flock($i2c->fh, LOCK_EX) or die "flock: $!";
$i2c->bus_write(...);
flock($i2c->fh, LOCK_UN) or die "flock: $!";