linux-kernel - Re: [PATCH v3 0/6] RTL8231 GPIO expander support

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Message-ID: <69c95adb6bafb8fbf69b9f79613606f62ba769e8.camel@svanheule.net>
Date:   Mon, 24 May 2021 17:20:13 +0200
From:   Sander Vanheule <sander@...nheule.net>
To:     Andy Shevchenko <andy.shevchenko@...il.com>
Cc:     Andrew Lunn <andrew@...n.ch>, Pavel Machek <pavel@....cz>,
        Rob Herring <robh+dt@...nel.org>,
        Lee Jones <lee.jones@...aro.org>,
        Mark Brown <broonie@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J . Wysocki" <rafael@...nel.org>,
        Michael Walle <michael@...le.cc>,
        Linus Walleij <linus.walleij@...aro.org>,
        Bartosz Golaszewski <bgolaszewski@...libre.com>,
        Linux LED Subsystem <linux-leds@...r.kernel.org>,
        devicetree <devicetree@...r.kernel.org>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 0/6] RTL8231 GPIO expander support

Hi Andy,

Forgot to reply to the sysfs suggestion.

On Mon, 2021-05-24 at 15:54 +0300, Andy Shevchenko wrote:
> On Mon, May 24, 2021 at 2:41 PM Sander Vanheule <sander@...nheule.net> wrote:
> > On Mon, 2021-05-24 at 10:53 +0300, Andy Shevchenko wrote:
> > > On Mon, May 24, 2021 at 4:11 AM Andrew Lunn <andrew@...n.ch> wrote:
> 
> > > > >   - Introduce GPIO regmap quirks to set output direction first
> > > > 
> > > > I thought you had determined it was possible to set output before
> > > > direction?
> > > 
> > > Same thoughts when I saw an updated version of that patch. My
> > > anticipation was to not see it at all.
> > 
> > The two devices I've been trying to test the behaviour on are:
> >  * Netgear GS110TPP: has an RTL8231 with three LEDs, each driven via a pin
> >    configured as (active-low) GPIO. The LEDs are easy for a quick visual
> > check.
> >  * Zyxel GS1900-8: RTL8231 used for the front panel button, and an active-
> > low
> >    GPIO used to hard reset the main SoC (an RTL8380). I've modified this
> > board
> >    to change some of the strapping pin values, but testing with the jumpers
> > and
> >    pull-up/down resistors is a bit more tedious.
> > 
> > On the Netgear, I tested the following with and without the quirk:
> > 
> >    # Set as OUT-LOW twice, to avoid the quirk. Always turns the LED on
> >    gpioset 1 32=0; gpioset 1 32=0
> >    # Get value to change to input, turns the LED off (high impedance)
> >    # Will return 1 due to (weak) internal pull-up
> >    gpioget 1 32
> >    # Set as OUT-HIGH, should result in LED off
> >    # When the quirk is disabled, the LED turns on (i.e. old OUT-LOW value)
> >    # When the quirk is enabled, the LED remains off (i.e. correct OUT-HIGH
> > value)
> >    gpioset 1 32=1
> > 
> > Now, what's confusing (to me) is that the inverse doesn't depend on the
> > quirk:
> > 
> >    # Set as OUT-HIGH twice
> >    gpioset 1 32=1; gpioset 1 32=1
> >    # Change to high-Z
> >    gpioget 1 32
> >    # Set to OUT-LOW, always results in LED on, with or without quirk
> >    gpioset 1 32=0
> > 
> > Any idea why this would be (or appear) broken on the former case, but not on
> > the
> > latter?
> 
> GPIO tools for the shell are context-less. Can you reproduce this with
> the legacy sysfs interface?

Using the sysfs interface produced the same behaviour for both test cases.

E.g. case 1:
   # Set to output low
   echo out > direction; echo 0 > value
   # Change to input (with weak pull-up)
   echo in > direction
   # Try to set to output high
   # Fails to go high if the pin value is set before the direction
   echo high > direction


Best,
Sander