Can't find Serial Number attribute for PL2303 device in linux

Question

When i run the following command after connecting PL2303 USB to serial converter to my ubuntu system:

dmesg | grep ttyUSB

i get:

usb 1-2: pl2303 converter now attached to ttyUSB0

then i run:

udevadm info -a -n /dev/ttyUSB0

i get:

looking at parent device '/devices/pci0000:00/0000:00:14.0/usb1/1-2':
KERNELS=="1-2"
SUBSYSTEMS=="usb"
DRIVERS=="usb"
ATTRS{authorized}=="1"
ATTRS{avoid_reset_quirk}=="0"
ATTRS{bConfigurationValue}=="1"
ATTRS{bDeviceClass}=="00"
ATTRS{bDeviceProtocol}=="00"
ATTRS{bDeviceSubClass}=="00"
ATTRS{bMaxPacketSize0}=="64"
ATTRS{bMaxPower}=="100mA"
ATTRS{bNumConfigurations}=="1"
ATTRS{bNumInterfaces}==" 1"
ATTRS{bcdDevice}=="0400"
ATTRS{bmAttributes}=="80"
ATTRS{busnum}=="1"
ATTRS{configuration}==""
ATTRS{devnum}=="27"
ATTRS{devpath}=="2"
ATTRS{idProduct}=="2303"
ATTRS{idVendor}=="067b"
ATTRS{ltm_capable}=="no"
ATTRS{manufacturer}=="Prolific Technology Inc. "
ATTRS{maxchild}=="0"
ATTRS{product}=="USB-Serial Controller D"
ATTRS{quirks}=="0x0"
ATTRS{removable}=="removable"
ATTRS{speed}=="12"
ATTRS{urbnum}=="20"
ATTRS{version}==" 1.10"

But no

ATTRS{serial} is found for the above PL2303 USB to serial converter. Can anyone please tell me why? I get the serial attribute for all other USB devices

Answer 1

The datasheet for the PL2303 serial converter chip includes a description of the EEPROM configuration data for the chip on page 11.

The EEPROM can specify the USB product and vendor IDs for the chip, so instead of using the generic USB-to-serial converter ID, someone using this chip in their products can use an ID that is specific to their product, allowing for seamless auto-detection and use of the product-specific driver, if desired. One would expect that the serial number might also be stored in that EEPROM. But there is no place for a serial number in the EEPROM data layout.

In fact, the entire datasheet does not document any way to retrieve an unique serial number from this serial converter at all. So I must conclude that this serial converter chip series simply does not have unique serial numbers, at least not in its earlier chip revisions (the datasheet is from year 2005).