linux-kernel - Re: [PATCH v4 3/3] USB: serial: cp210x: Workaround cp2108 GET_LINE

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Date:	Thu, 29 Oct 2015 08:39:04 -0500
From:	Konstantin Shkolnyy <konstantin.shkolnyy@...il.com>
To:	Johan Hovold <johan@...nel.org>
Cc:	linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 3/3] USB: serial: cp210x: Workaround cp2108
 GET_LINE_CTL bug

I tested it on cp2102, cp2105 and cp2108.
I'm a little worried about that extra PURGE command, so I did several
manual tests on each with a standard PC serial port on the other end
of the cable.
- run several open/write/close iteration (the test that used to break
cp2108), observe data on the other end;
- open minicom and see that cp210x can still receive data from the other end.

BTW, can you suggest (preferably automated) serial port test s/w?

On Thu, Oct 29, 2015 at 2:19 AM, Johan Hovold <johan@...nel.org> wrote:
> On Wed, Oct 28, 2015 at 09:51:26AM +0100, Johan Hovold wrote:
>> On Tue, Oct 27, 2015 at 04:53:34PM -0500, Konstantin Shkolnyy wrote:
>> > cp2108 GET_LINE_CTL returns the 16-bit value with the 2 bytes swapped.
>> > However, SET_LINE_CTL functions properly. When the driver tries to modify
>> > the register, it reads it, modifies some bits and writes back. Because the
>> > read bytes were swapped, this often results in an invalid value to be
>> > written. In turn, this causes cp2108 respond with a stall. The stall
>> > sometimes doesn't clear properly and cp2108 starts responding to following
>> > valid commands also with stalls, effectively failing.
>> >
>> > Signed-off-by: Konstantin Shkolnyy <konstantin.shkolnyy@...il.com>
>
>> I gave the series a really quick test on an cp2102-device I had lying
>> around. I assume you verified the changes on some other older devices as
>> well?
>
> Did you test this series on the older device types as well?
>
> Thanks,
> Johan
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