linux-kernel - Re: [PATCH v2] USB: serial: cp210x: Fix GPIO in autosuspend

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Message-ID: <c936ea8404f192276e0a42d9da0b7863@pados.hu>
Date:   Tue, 19 Mar 2019 17:12:25 +0000
From:   "Karoly Pados" <pados@...os.hu>
To:     "Oliver Neukum" <oneukum@...e.com>,
        "Johan Hovold" <johan@...nel.org>
Cc:     "Loic Poulain" <loic.poulain@...aro.org>,
        "Greg Kroah-Hartman" <gregkh@...uxfoundation.org>,
        linux-kernel@...r.kernel.org, linux-usb@...r.kernel.org
Subject: Re: [PATCH v2] USB: serial: cp210x: Fix GPIO in autosuspend

Hi Oliver,

USB suspend does not turn off power. Your concerns about the situations you list
are valid, but my patch is for another problem. Not for what happens
when power is lost, but because the user couldn't use the GPIO lines even if
power was on and continous, due to the kernel automatically putting the device into
suspend and then all usb messages failed in this case.

Karoly

March 19, 2019 12:26 PM, "Oliver Neukum" <oneukum@...e.com> wrote:

> On Di, 2019-03-19 at 11:36 +0100, Johan Hovold wrote:
> 
>> On Mon, Feb 18, 2019 at 10:17:12AM +0100, Oliver Neukum wrote:
>> On So, 2019-02-17 at 18:59 +0100, Karoly Pados wrote:
>>> Current GPIO code in cp210x fails to take USB autosuspend into account,
>>> making it practically impossible to use GPIOs with autosuspend enabled
>>> without user configuration. Fix this like for ftdi_sio in a previous patch.
>>> Tested on a CP2102N.
>> your patch is looking good to me, but I am afraid there are issues.
>> How do the GPIO lines on the device interact with USB reset and system
>> suspend?
>> 
>> What was your concern here, Oliver?
> 
> If you have a device resetting or losing power (for reset_resume) the
> GPIO lines will revert to the default. But that change is not reported
> to user space, is it?
> So the original patch is correct, but there are more situations rather
> than suspend which could trigger the problem.
> 
> Regards
> Oliver