drivers: stepper: Add stepper driver for allegro a4988

[Hallootto1100]

This PR adds a stepper driver for allegro a4988 DMOS microstepping driver.

It has manly be copied from the gpio_stepper_controller and adapted where needed.
I've tested it using the stepper_shell.

One can enable this driver in an overlay like follow:

stepper: a4988 {
        compatible = "allegro,a4988";
        dir-gpios = <&gpio0 22 0>;
        step-gpios = <&gpio0 23 0>;
        en-gpios = <&gpio0 5 0>;
        msx-gpios = <&gpio0 15 0>, 
                    <&gpio0 2 0>, 
                    <&gpio0 4 0>;
    };

en-gpios and msx-gpios (used for selecting micro stepping mode) are optional and can be left away.

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[jilaypandya]

Thanks for the contribution,

• Could you write a generic driver with step_dir interface? For instance, a4988, drv8825 and quite a few other drivers have this same interface.
• Also i can see right now its a bitbang driver, however, as far as i understand you could also use pwm for stepper control, use the step pin.

[Hallootto1100]

Could you write a generic driver with step_dir interface? For instance, a4988, drv8825 and quite a few other drivers have this same interface.

In theory I think yes.
I was not sure about the micro stepping resolution gpios and if they are handled on all stepper drivers the same way.
(e.g. the a4988 has a strange value for setting 16th steps.)
And then many driver have some additional functionalities. E.g. sleep mode and fault detection.

Also i can see right now its a bitbang driver, however, as far as i understand you could also use pwm for stepper control, use the step pin.

That came also to my mind during development. However, I haven't used the pwm api as much and wanted to finish this for now.

Also i see that a lot of code has been carried over from gpio_stepper_controller. These two drivers could be unified in the future. Using Kconfig one can select between GPIO_STEPPER STEP_DIR_PWM_STEPPER or STEP_DIR_GPIO_STEPPER

Yes, that would make sense since a lot of the code is shared.

[pdgendt]

Add an entry to tests/drivers/build_all/stepper/

[Hallootto1100]

Hi @Hallootto1100,

Can you update the existing gpio_stepper_controller to accomodate this interface. I see a lot of code is carried over from that controller. We can update the existing dts bindings and use kconfig variables to select between various interfaces.

This idea was floated in the community in the past and now i clearly see merit in doing so.

@jilaypandya I might find some time next Friday.

[jilaypandya]

Yes, that would make sense since a lot of the code is shared.

A minor correction on my side, this selection would have to be in device tree. Because in theory you could have two different types of gpio driver and selection of interface would have to be device driver specific.