linux-kernel - Re: [PATCH] hte: tegra194: improve the GPIO-related comment

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Message-ID: <CAMRc=MeWXapho1bsX9Si5uSx7MWVhpT2cqrv5S+qPo51Ko=Vtg@mail.gmail.com>
Date:   Mon, 2 Oct 2023 10:33:02 +0200
From:   Bartosz Golaszewski <brgl@...ev.pl>
To:     Dipen Patel <dipenp@...dia.com>
Cc:     Thierry Reding <thierry.reding@...il.com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        timestamp@...ts.linux.dev, linux-tegra@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Bartosz Golaszewski <bartosz.golaszewski@...aro.org>,
        Linus Walleij <linus.walleij@...aro.org>
Subject: Re: [PATCH] hte: tegra194: improve the GPIO-related comment

On Fri, Sep 29, 2023 at 11:38 PM Dipen Patel <dipenp@...dia.com> wrote:
>
> On 9/11/23 2:44 AM, Bartosz Golaszewski wrote:
> > From: Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
> >
> > Using any of the GPIO interfaces using the global numberspace is
> > deprecated. Make it clear in the comment.
> >
> > Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
> > Acked-by: Linus Walleij <linus.walleij@...aro.org>
> > ---
> > This was part of a wider series but since this is independent, I'm sending
> > it separately.
> >
> >  drivers/hte/hte-tegra194.c | 13 ++++++++-----
> >  1 file changed, 8 insertions(+), 5 deletions(-)
> >
> > diff --git a/drivers/hte/hte-tegra194.c b/drivers/hte/hte-tegra194.c
> > index 6fe6897047ac..9fd3c00ff695 100644
> > --- a/drivers/hte/hte-tegra194.c
> > +++ b/drivers/hte/hte-tegra194.c
> > @@ -407,12 +407,15 @@ static int tegra_hte_line_xlate(struct hte_chip *gc,
> >               return -EINVAL;
> >
> >       /*
> > +      * GPIO consumers can access GPIOs in two ways:
> >        *
> > -      * There are two paths GPIO consumers can take as follows:
> > -      * 1) The consumer (gpiolib-cdev for example) which uses GPIO global
> > -      * number which gets assigned run time.
> > -      * 2) The consumer passing GPIO from the DT which is assigned
> > -      * statically for example by using TEGRA194_AON_GPIO gpio DT binding.
> > +      * 1) Using the global GPIO numberspace.
> > +      *
> > +      * This is the old, now DEPRECATED method and should not be used in
> > +      * new code. TODO: Check if tegra is even concerned by this.
> This use case is to do namespace mapping from gpio subsystem to hte. Few doubts:
> 1. What does deprecate mean here? Does gpio subsys not use global space anymore?

It does but we don't want to expose this to external users in any way
anymore (and haven't to for years). This is what deprecated means.
Users should deal with opaque GPIO descriptors not global GPIO
numberspace.

> 2. If yes, what GPIO number is set when it comes from gpiolib-cdev, as based on that I may have to
> reflect in the mapping, tegra194_aon_gpio_map for example.

Why DO you have to use a GPIO number though? If HTE needs just a
number from some HTE numberspace (which in itself may be unnecessary)
then why not just keep a local IDA for it? Do you have to know the
GPIOs internal numbering scheme to make it work?

Bart

> > +      *
> > +      * 2) Using GPIO descriptors that can be assigned to consumer devices
> > +      * using device-tree, ACPI or lookup tables.
> >        *
> >        * The code below addresses both the consumer use cases and maps into
> >        * HTE/GTE namespace.
>