Re: [PATCH] Revert "USB: serial: ch341: add new Product ID for CH341A"

[Johan Hovold <johan@kernel.org>]

On Thu, Feb 10, 2022 at 07:41:22AM +0200, Dmytro Bagrii wrote:
> On 09.02.22 16:18, Johan Hovold wrote:

> > I don't remember all the details, but judging from a quick look it seems
> > we're just waiting for someone to resend the revert with a proper
> > explanation.
> > 
> > It would be good if Jan-Niklas could chime in too and confirm if he's
> > able to use the device in UART mode instead.
> 
> I'd like to take a look at that keeyees device from original commit 
> message to see if it has EEPROM chip. I can hypothesize that some 
> manufacturer of a CH341-based programmer could use external configuration 
> EEPROM and mixed-up PID value. I haven't experiment with configuring 
> CH341A with EEPROM but suppose it's possible to burn any custom VID:PID 
> there. I don't think ch341 driver has to handle any of such custom 
> VID/PID, especially if it conflicts with an original VID/PID assigned by 
> chip manufacturer. In case of some peculiar devices it's possible to bind 
> custom VID:PID to the driver via sysfs.
> 
> But it's just my hypothetical assumption how ch341-based device with PID 
> 5512 could work as UART in that case.
> 
> I just checked if CH341 that i have can work as UART when configured as 
> I2C/SPI (PID 5512). I doesn't work: no output signal on TX pin, no 
> loopback echo when RX connected to self TX.

Thanks for confirming.

Johan