linux-kernel - Re: [PATCH v10 2/5] gpio: sim: new testing module

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Date:   Thu, 25 Nov 2021 14:14:20 +0100
From:   Bartosz Golaszewski <brgl@...ev.pl>
To:     Kent Gibson <warthog618@...il.com>,
        Linus Walleij <linus.walleij@...aro.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:     "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v10 2/5] gpio: sim: new testing module

On Wed, Nov 24, 2021 at 12:43 PM Bartosz Golaszewski <brgl@...ev.pl> wrote:
>
> Implement a new, modern GPIO testing module controlled by configfs
> attributes instead of module parameters. The goal of this driver is
> to provide a replacement for gpio-mockup that will be easily extensible
> with new features and doesn't require reloading the module to change
> the setup.
>
> Signed-off-by: Bartosz Golaszewski <brgl@...ev.pl>
> ---
>  Documentation/admin-guide/gpio/gpio-sim.rst |   80 ++
>  drivers/gpio/Kconfig                        |    8 +
>  drivers/gpio/Makefile                       |    1 +
>  drivers/gpio/gpio-sim.c                     | 1370 +++++++++++++++++++
>  4 files changed, 1459 insertions(+)
>  create mode 100644 Documentation/admin-guide/gpio/gpio-sim.rst
>  create mode 100644 drivers/gpio/gpio-sim.c
>

Hi guys!

I'd like to get your opinion on some parts of the interface.

Should we allow creating multiple gpiochips per platform device like
some drivers do? And if so - should the sysfs groups be created for
each gpiochip device kobject and not the parent?

Currently we do this:

# Create the chip (platform device + single gpiochip):
mkdir /sys/kernel/config/gpio-sim/my-chip
# Configure it
echo 8 > /sys/kernel/config/gpio-sim/my-chip/num_lines
# Enable it
echo 1 > /sys/kernel/config/gpio-sim/my-chip/live

What I mean above would make it look like this:

# Create the platform device
mkdir /sys/kernel/config/gpio-sim/my-gpio-device

# what's inside?
ls /sys/kernel/config/gpio-sim/my-gpio-device
live

# Create GPIO chips
mkdir /sys/kernel/config/gpio-sim/my-gpio-device/chip0
mkdir /sys/kernel/config/gpio-sim/my-gpio-device/chip1

# Configure chips
echo 8 > /sys/kernel/config/gpio-sim/my-gpio-device/chip0/num_lines
echo 4 > /sys/kernel/config/gpio-sim/my-gpio-device/chip1/num_lines
echo foobar > /sys/kernel/config/gpio-sim/my-gpio-device/chip1/label

# Enable both chips
echo 1 > /sys/kernel/config/gpio-sim/my-gpio-device/live

And in sysfs instead of current:

echo pull-up > /sys/devices/platform/gpio-sim.0/sim_line0/pull

We'd have to do:

echo pull-up > /sys/devices/platform/gpio-sim.0/gpiochip1/sim_line0/pull

While I don't see any usefulness of that at this time, if we don't do
it now, then it'll be hard to extend this module later. What are your
thoughts?

Bart