Re: [PATCH v4] media: rc: pwm-ir-tx: Switch to atomic PWM API

[Sean Young <sean@mess.org>]

On Thu, Oct 28, 2021 at 08:45:13AM +0200, Uwe Kleine-König wrote:
> The conversion is right (I think),

We still have the problem that the pwm drivers calculate the period
incorrectly by rounding down (except pwm-bcm2835). So the period is not
as good as it could be in most cases, but this driver can't do anything
about that.

> note this could be optimized a bit
> further: state.period only depends on carrier which rarely changes, so
> the calculation could be done in pwm_ir_set_carrier(). Ditto for duty
> which only depends on state.period and pwm_ir->duty_cycle. (This is for
> a separate commit though.)

I'm not sure what caching this is much of a win. The calculation is a few
instructions, so you're not winning in the way of speed. On the flip side
you use more memory since pwm_state has to be kmalloc() rather than existing
just on the stack, and both ioctl handlers and the probe function need to
recalculate the period/duty cycle, so there is a slight increase in code size.

This change does not improve anything measurably and only increases code
complexity.

> Acked-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>

Thanks for your review.


Sean