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

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Message-ID: <CAHp75Vf_dAfoMmziVLkEQ2Yr-e7Cj5=61ua5Q05Cyz-pLwVjpw@mail.gmail.com>
Date:   Mon, 24 May 2021 15:54:37 +0300
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     Sander Vanheule <sander@...nheule.net>
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

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:

...

> > > > Changes since v2:
> > > >   - MDIO regmap support was merged, so patch is dropped here
> > >
> > > Do you have any idea how this will get merged. It sounds like one of
> > > the Maintainers will need a stable branch of regmap.
> >
> > This is not a problem if Mark provides an immutable branch to pull from.
>
> Mark has a tag (regmap-mdio) for this patch:
> https://git.kernel.org/pub/scm/linux/kernel/git/broonie/regmap.git/tag/?h=regmap-mdio

Also works but you have to provide this information in the cover letter.

...

> > > >   - 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?

> I was trying to reproduce this behaviour on the Zyxel, but using the strapping
> pins that are also used to configure the device's address. So perhaps the pull-
> ups/-downs were confusing the results. Using a separate pin on the Zyxel's
> RTL8231, I've now been able to confirm the same behaviour as on the Netgear,
> including capturing the resulting glitch (with my simple logic analyser) when
> enabling the quirk in the first test case.
>
> I hope this explains why I've still included the quirk in this revision. If not,
> please let me know what isn't clear.

Do you possess a schematic of either of the devices and a link to the
RTL datasheet (Btw, if it's publicly available, or you have a link
that will ask for necessary sign-in it would be nice to include the
link to it as a Datasheet: tag)?

-- 
With Best Regards,
Andy Shevchenko