PWM-GPIO driver: how to configure it?

PWM-GPIO driver: how to configure it?

[Jean-Michaël Celerier]

Hello!

I am curious of trying the new pwm-gpio driver in Linux 6.11 with a
Diolan DLN-2 chip, which exposes a gpiochip accessible to linux over
USB.

I haven't managed to see where the configuration options of the driver
are set: for instance, let's say I want to create a PWM output channel
over gpiochip1 line 4, 6 and 12, what should my modprobe line look
like ?

Kind regards,

------
Jean-Michaël Celerier
Société des Arts Technologiques

Re: PWM-GPIO driver: how to configure it?

[Kent Gibson]

On Wed, Oct 02, 2024 at 02:41:06PM -0400, Jean-Michaël Celerier wrote:
> Hello!
>

This is probably best asked on the PWM list, so cross-posting.

> I am curious of trying the new pwm-gpio driver in Linux 6.11 with a
> Diolan DLN-2 chip, which exposes a gpiochip accessible to linux over
> USB.
>
> I haven't managed to see where the configuration options of the driver
> are set: for instance, let's say I want to create a PWM output channel
> over gpiochip1 line 4, 6 and 12, what should my modprobe line look
> like ?
>

Good question.
I think it has to be setup by device tree, but that is just a guess.

Cheers,
Kent.

Re: PWM-GPIO driver: how to configure it?

[Uwe Kleine-König]

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Hello,

On Fri, Oct 04, 2024 at 03:06:55PM +0800, Kent Gibson wrote:
> On Wed, Oct 02, 2024 at 02:41:06PM -0400, Jean-Michaël Celerier wrote:
> 
> This is probably best asked on the PWM list, so cross-posting.
> 
> > I am curious of trying the new pwm-gpio driver in Linux 6.11 with a
> > Diolan DLN-2 chip, which exposes a gpiochip accessible to linux over
> > USB.
> >
> > I haven't managed to see where the configuration options of the driver
> > are set: for instance, let's say I want to create a PWM output channel
> > over gpiochip1 line 4, 6 and 12, what should my modprobe line look
> > like ?
> 
> Good question.
> I think it has to be setup by device tree, but that is just a guess.

Setting up the pwm-gpio device via device tree only works if you manage
to describe the USB gpio chip in the device tree, too, as teh pwm-gpio
device must have valid gpio descriptors.

Otherwise you'd need to extend the pwm-gpio driver to instantiate
devices dynamically somehow.

Best regards
Uwe

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Re: PWM-GPIO driver: how to configure it?

[Jean-Michaël Celerier]

Thanks, my understanding is then that it is not really possible as of
now to instantiate this driver with hot-plug USB devices, right ?
I'd gladly look into contributing a patch but have never contributed
to the kernel and would have no clue as to where to start.

Kind regards,
Jean-Michaël

Re: PWM-GPIO driver: how to configure it?

[Uwe Kleine-König]

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Hello Jean-Michaël,

On Fri, Oct 04, 2024 at 09:59:00AM -0400, Jean-Michaël Celerier wrote:
> Thanks, my understanding is then that it is not really possible as of now
> to instantiate this driver with hot-plug USB devices, right ?

Not 100% sure. It's possible to add information for pci devices to the
device tree, too, even though that bus is hotpluggable and usually
autodetected.

> I'd gladly look into contributing a patch but have never contributed to the
> kernel and would have no clue as to where to start.

For the generic solution you would need to create a sysfs file similar
to the "new_device" property for i2c (implemented in
drivers/i2c/i2c-core-base.c:new_device_store()). Instead of creating a
i2c device you'd create a platform device then. But the details are
different enough that this isn't an easy task for a kernel newcomer.

Best regards
Uwe

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