linux-kernel - Re: [PATCH v2 1/2] Revert "USB: serial: ch341: add new Product ID for CH341A"

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Message-ID: <8b3c348f-9e05-29f9-9197-8ddf1c8a9e8b@zago.net>
Date:   Tue, 11 May 2021 20:07:31 -0500
From:   Frank Zago <frank@...o.net>
To:     Johan Hovold <johan@...nel.org>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-kernel@...r.kernel.org,
        Jan-Niklas Burfeind <kernel@...ionpri.me>,
        Bartosz Golaszewski <bgolaszewski@...libre.com>,
        Wolfram Sang <wsa@...nel.org>, linux-usb@...r.kernel.org,
        gunar@...orcht.net
Subject: Re: [PATCH v2 1/2] Revert "USB: serial: ch341: add new Product ID for
 CH341A"

Hello,

On 5/10/21 2:40 AM, Johan Hovold wrote:
> On Thu, Apr 22, 2021 at 07:28:51PM -0500, Frank Zago wrote:
>> From: frank zago <frank@...o.net>
>> 
>> The 0x5512 USB PID is for the I2C/GPIO/SPI interfaces. UART is 
>> still present but only the TX and RX pins are available; DTS, DTR, 
>> ... are used for other things. Remove the PID, and let a I2C
>> driver bind to it.
>> 
>> Existing CH341 boards usually have physical jumpers to switch 
>> between the 3 modes.
>> 
>> This reverts commit 46ee4abb10a07bd8f8ce910ee6b4ae6a947d7f63.
> 
> You can't just revert something which people clearly depend on and 
> therefore added to the kernel in the first place.

That device in UART mode was already supported by the serial driver. The 
original submitter just had to move a jumper on his board. There was no 
need to patch the kernel.

That product ID also supports UART but in a limited way, as only the RX and TX
pins are available. However it is the only one that supports i2c/spi/gpio, and
that's why I have to revert the patch. 

If that's desired, the new driver could add support for that as well, but I don't
think it's worth the effort.

> 
> Can you reprogram the device with a newly allocated PID to be used 
> for i2c-only instead?

It is possible if the device has an SPI flash connected to it, but none of
the cheap boards have that.

Frank.