Re: [PATCH 8/8] pwm: Add support for pwmchip devices for faster and easier userspace access

[Kent Gibson <warthog618@gmail.com>]

On Sun, Mar 17, 2024 at 11:40:39AM +0100, Uwe Kleine-König wrote:
> With this change each pwmchip can be accessed from userspace via a
> character device. Compared to the sysfs-API this is faster (on a
> stm32mp157 applying a new configuration takes approx 25% only) and
> allows to pass the whole configuration in a single ioctl.
>
> Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>

> new file mode 100644
> index 000000000000..ca765bfaa68d
> --- /dev/null
> +++ b/include/uapi/linux/pwm.h
> @@ -0,0 +1,23 @@
> +/* SPDX-License-Identifier: GPL-2.0-only WITH Linux-syscall-note */
> +
> +#ifndef _UAPI_PWM_H_
> +#define _UAPI_PWM_H_
> +
> +#include <linux/ioctl.h>
> +#include <linux/types.h>
> +
> +struct pwmchip_state {
> +	unsigned int hwpwm;
> +	__u64 period;
> +	__u64 duty_cycle;
> +	__u64 duty_offset;
> +};
> +

Sorry for being late to the party, but I only ran across this thread by
accident.

Have you considered the implications of sizing and alignment here[1]?

Change this to:

struct pwmchip_state {
	__u32 hwpwm;
    __u32 __pad;
	__u64 period;
	__u64 duty_cycle;
	__u64 duty_offset;
};

to clarify?

Cheers,
Kent.

[1] https://docs.kernel.org/driver-api/ioctl.html#bit-compat-mode (and
subsequent sections)