Re: [PATCH 1/4] pwm: Make of_pwm_xlate_with_flags() work with #pwm-cells = <2>

[Thierry Reding <thierry.reding@gmail.com>]

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On Mon, Mar 15, 2021 at 12:11:21PM +0100, Uwe Kleine-König wrote:
> The two functions of_pwm_simple_xlate() and of_pwm_xlate_with_flags() are
> quite similar. of_pwm_simple_xlate() only supports two pwm-cells while
> of_pwm_xlate_with_flags() only support >= 3 pwm-cells. The latter can
> easily be modified to behave identically to of_pwm_simple_xlate for two
> pwm-cells. This is implemented here and allows to drop
> of_pwm_simple_xlate() in the next commit.
> 
> There is a small detail that is different now between of_pwm_simple_xlate()
> and of_pwm_xlate_with_flags() with pwm-cells = <2>: pwm->args.polarity is
> unconditionally initialized to PWM_POLARITY_NORMAL in the latter. I didn't
> find a case where this matters and doing that explicitly is the more
> robust approach.
> 
> Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
> ---
>  drivers/pwm/core.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/pwm/core.c b/drivers/pwm/core.c
> index b1adf3bb8508..39b0ad506bdd 100644
> --- a/drivers/pwm/core.c
> +++ b/drivers/pwm/core.c
> @@ -126,8 +126,7 @@ of_pwm_xlate_with_flags(struct pwm_chip *pc, const struct of_phandle_args *args)
>  {
>  	struct pwm_device *pwm;
>  
> -	/* check, whether the driver supports a third cell for flags */
> -	if (pc->of_pwm_n_cells < 3)
> +	if (pc->of_pwm_n_cells < 2)
>  		return ERR_PTR(-EINVAL);
>  
>  	/* flags in the third cell are optional */
> @@ -144,7 +143,8 @@ of_pwm_xlate_with_flags(struct pwm_chip *pc, const struct of_phandle_args *args)
>  	pwm->args.period = args->args[1];
>  	pwm->args.polarity = PWM_POLARITY_NORMAL;
>  
> -	if (args->args_count > 2 && args->args[2] & PWM_POLARITY_INVERTED)
> +	if (pc->of_pwm_n_cells >= 3 && args->args_count > 2 &&
> +	    args->args[2] & PWM_POLARITY_INVERTED)

This might more clearly look like a superset of of_pwm_xlate_simple() if
you split up the conditional this way:

	if (pc->of_pwm_n_cells >= 3) {
		if (args->args_count > 2 && args->args[2] & PWM_POLARITY_INVERTED)
			...
	}

That'd also help if we ever end up extending the list of supported
flags.

Thierry

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