Apparently, hplip does not support USB to parallel adapters - see for example http://firstname.lastname@example.org/msg02858.html
I managed to get a parallel printer connected via a PL2305 adapter like yours to work with CUPS by manually editing the printers.conf file as described by @Sandro kensan - I am looking at the CUPS 'Printer Test Page' right now, so I can confirm that Sandro kensan's method works.
I suspect that the absence of printers.conf on your machine means that you do not have CUPS installed. I recommend you do not attempt to create this entire file from scratch; it consists of much more than a single line.
As for HPLIP - I have been completely unable to get it to recognise my LaserJet 2100 connected via a PL2305. What follows is what I've tried so far, in the hope it saves you some time.
Firstly, I tried specifying the USB bus:device numbers of the PL2305 to hp-setup's command line. That results in hp-setup walking the entire USB device tree, at times reading data from USB devices then closing them again, then finally outputting
error: No device selected/specified or that supports this functionality.
and exiting with nonzero status. I suspect it was sniffing each device to see whether it smelt like an HP printer, deciding none were, and giving up.
Secondly, I tried to set the printer up as a parallel printer. Comments elsewhere online said this would not work but as USB had already failed I decided to try it.
The first problem you encounter with this approach is that hp-setup wants to scan rather than be told the device node to use. To defeat this, you have to run it from the command line and supply the device node as an argument.
The next problem is that hp-setup only recognises the command-line argument as a parallel port device node (as opposed, for example, to a USB bus:device ID) if it is in the form /dev/partport[0-9]. I defeated that by doing:
sudo ln -s /dev/usb/lp1 /dev/parport1
That could be made persistent using a custom udev rule, but it's an ugly hack.
The next problem is that the HPLIP tools then (rightly) assume that /dev/parport1 is an lp device, and issue parallel-specific ioctls such as PPGETMODES on it. The kernel driver for the PL2305 is not 'parallel-ish' enough to understand these, so returns an error code, which causes the HPLIP tools to skip that device node, in the process outputting more cryptic/useless diagnostics such as:
Invalid device URI
As far as I can tell, HPLIP wants to see either:
- A USB device which is an HP brand printer (not a adaptor/bridge behind which sits a printer); or
- An 'lp'-like device node representing a parallel port, which supports all of the parallel-specific ioctls.
The /dev/usb/lp[0-9] device nodes we get when we plug in our PL2305s are neither of these, and HPLIP can't handle them itself, and is inflexible such that it supplies no way I can see for you to force it to Do The Right Thing.