linux-kernel - Re: [PATCH v3] pinctrl: tegra: Add support to display pin function

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Date:   Fri, 29 Sep 2023 14:26:47 +0200
From:   Thierry Reding <thierry.reding@...il.com>
To:     Luca Ceresoli <luca.ceresoli@...tlin.com>
Cc:     Linus Walleij <linus.walleij@...aro.org>,
        Prathamesh Shete <pshete@...dia.com>, jonathanh@...dia.com,
        linux-gpio@...r.kernel.org, linux-tegra@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] pinctrl: tegra: Add support to display pin function

On Thu, Sep 28, 2023 at 08:53:19AM +0200, Luca Ceresoli wrote:
> Hello Linus, Prathamesh,
> 
> On Wed, 27 Sep 2023 10:54:15 +0200
> Linus Walleij <linus.walleij@...aro.org> wrote:
> 
> > On Mon, Sep 25, 2023 at 6:30 PM Luca Ceresoli <luca.ceresoli@...tlin.com> wrote:
> > 
> > > The symptom is that i2c3 is not working anymore, the I2C lines being
> > > always high. No other known issues at the moment.  
> > 
> > Hm....
> > 
> > >> +     {"nvidia,function",             TEGRA_PINCONF_PARAM_FUNCTION},  
> > >
> > > FYI, I reduced your patch to only this line plus the one in the
> > > pinctrl-tegra.h and the problem appears as well.  
> > 
> > I think there is a conflict now, that the pinconf is "stealing" the function
> > assignment from the pinmux call.
> > 
> > It's just a debugprint, I will revert the patch, Luca can investigate and you
> 
> Thanks for the quick revert Linus.
> 
> > can test a new patch then we will merge that.
> 
> Prathamesh, if you send a new patch it would be great if you can Cc: me so I
> can test it.

I was able to reproduce this on tegra20-trimslice, and it looks indeed
that the "shortcut" of supporting this through the pinconf "framework"
doesn't work. In addition to the pinmux now no longer getting applied
(exactly why that is I don't think I understand), it also leads to weird
things in other parts of the debugfs output. For example the code now
ends up trying to read a u32 from the nvidia,function property, which is
actually a string. That seems to be fine, but obviously it doesn't yield
the value that is expected for a function and messes up the config param
which will then later on fail to properly display.

Anyway, turns out the correct implementation is even shorter. I've sent
out a patch.

Thierry

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