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PL2303 variant TechToo USB to Serial adapter ... FYI
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eccerr0r
Watchman
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Joined: 01 Jul 2004
Posts: 9883
Location: almost Mile High in the USA

PostPosted: Mon Jan 31, 2022 1:53 am    Post subject: PL2303 variant TechToo USB to Serial adapter ... FYI Reply with quote

FYI...

It appears that Prolific made another variant of their PL2303 usb-serial chips that doesn't detect under the old versions of the Linux kernel driver. Appears that the one in 5.4.97 does not have support but 5.10.76 does. Symptom is that it shows up in USB enumeration but does not detect with the pl2303.ko driver. The new variant appears to be slightly different and has a vendor:product ID of 067B:23C3. Hacking the product ID into the driver "sort of" works for old kernels, I haven't tried the 5.10 driver yet...

So if you find your kernel detecting the PL2303 but not attach it to /dev/ttyUSB*, you may have an old driver, and upgrading will remedy the issue.

The one I got that fails to detect with the old driver at least appears to have a serial number in the USB fields so I can more easily detect this serial adapter through udev. I have two other PL2303's that are pretty much identical and thus makes it hard to tell the difference between the two in udev, and the only way to tell is through which host controller... if on the same host controller and on the same hub, it makes it mighty hard to tell which is which.
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spica
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Joined: 04 Jun 2021
Posts: 339

PostPosted: Mon Jan 31, 2022 3:04 pm    Post subject: Reply with quote

According to git history, 0x23c3 was added in v5.5

https://github.com/torvalds/linux/blob/master/drivers/usb/serial/pl2303.h#L14
Code:
#define PL2303_VENDOR_ID   0x067b
#define PL2303_PRODUCT_ID_GT      0x23c3
git blame https://github.com/torvalds/linux/blame/master/drivers/usb/serial/pl2303.c#L52
There's a link on a left pane, https://github.com/torvalds/linux/commit/ebd09f1cd417fce9c85de3abcabf51eadf907a2a and it shows the nearest tag 5.5-rc1
In order to make sure the change was accepted in v5.5, need to check changelog https://kernelnewbies.org/Linux_5.5#Universal_Serial_Bus (search for 2303)

It looks like some new logic was added too; at least, the commit contains more than just dev/vendor id addition
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