linux-kernel - Re: Likely issue with ch341 kernel-module/driver

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Date:	Thu, 27 Aug 2015 14:03:00 +0200
From:	Peter Stuge <peter@...ge.se>
To:	Johan Hovold <johan@...nel.org>
Cc:	Ajay Garg <ajaygargnsit@...il.com>, linux-kernel@...r.kernel.org,
	linux-usb@...r.kernel.org
Subject: Re: Likely issue with ch341 kernel-module/driver

Johan Hovold wrote:
> > I started in the morning to build the driver from the source provided
> > by the vendor, but it was written in the times of kernel-version 2.4,
> > and I got hopelessly stuck.
> 
> The vendor driver is only for 2.4? Peter?

http://www.wch.cn/download/CH341SER_LINUX_ZIP.html
http://www.wch.cn/downfile/177

The vendor driver version 1.2 readme.txt from 2014-10-10 says:

Current Driver support versions of linux kernel range from 2.6.25 to 3.13.x

It didn't build immediately against the kernel I had at hand, but with
a small touchup (patch attached) it built fine against a 3.10 kernel.

> > Also, as per http://lxr.free-electrons.com/source/drivers/usb/serial/ch341.c?v=3.16,
> > the particular serial-USB-adapter device is added into the id_table,
> > so seems supported as per say.
> 
> That id was added by 82078234d402 ("USB: serial: ch341: New VID/PID for
> CH341 USB-serial") in 2008, which claims that the driver supports both
> old and new devices.

My hardware has that same VID/PID, but there is a version request
sent to the device and my version number is quite a bit higher (20-30)
than what is mentioned in the in-tree driver comments; I guess the
protocol grew with newer versions of the device, but VID/PID weren't
updated. I'm sure it's possible to have a backwards-compatible
driver, but the vendor driver differs enough from the in-tree driver
that I can't be confident that simply doing what the vendor driver
does will work also on older versions of the device.

> > ###########################################################
> > usb 2-2: device not accepting address 8, error -71
> > ###########################################################
> 
> This still looks like a hardware issue to me. Specifically, this happens
> before the ch341 driver is even involved.

I haven't seen any messages like this with my hardware.

//Peter

View attachment "touchup-ch34x.c-version-1.2-for-linux-3.10.patch" of type "text/plain" (5314 bytes)