On Thu, Nov 25, 2021 at 02:14:20PM +0100, Bartosz Golaszewski wrote:

On Wed, Nov 24, 2021 at 12:43 PM Bartosz Golaszewski [off-list ref] wrote:

quoted

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 <redacted>
---
 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?

I might be missing something, but I don't see the platform abstraction
adding anything that can't be easily emulated in userspace using multiple
chips, and it complicates the minimal case as you now have to create a
platform as well as the chip.
So I'd keep it simple and stick with the chip level abstraction.

Cheers,
Kent.