linux-kernel - Re: [PATCH v5 1/2] pwm: Introduce single-PWM of

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Date:   Fri, 24 Sep 2021 09:16:52 +0200
From:   Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
To:     Bjorn Andersson <bjorn.andersson@...aro.org>
Cc:     Thierry Reding <thierry.reding@...il.com>,
        Lee Jones <lee.jones@...aro.org>,
        Andrzej Hajda <a.hajda@...sung.com>,
        Neil Armstrong <narmstrong@...libre.com>,
        Robert Foss <robert.foss@...aro.org>,
        Laurent Pinchart <Laurent.pinchart@...asonboard.com>,
        Jonas Karlman <jonas@...boo.se>,
        Jernej Skrabec <jernej.skrabec@...il.com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        linux-pwm@...r.kernel.org, Doug Anderson <dianders@...gle.com>
Subject: Re: [PATCH v5 1/2] pwm: Introduce single-PWM of_xlate function

On Thu, Sep 23, 2021 at 09:12:24PM -0500, Bjorn Andersson wrote:
> The existing pxa driver and the upcoming addition of PWM support in the
> TI sn565dsi86 DSI/eDP bridge driver both has a single PWM channel and
> thereby a need for a of_xlate function with the period as its single
> argument.
> 
> Introduce a common helper function in the core that can be used as
> of_xlate by such drivers and migrate the pxa driver to use this.
> 
> Signed-off-by: Bjorn Andersson <bjorn.andersson@...aro.org>
> ---
> 
> Changes since v4:
> - None
> 
>  drivers/pwm/core.c    | 26 ++++++++++++++++++++++++++
>  drivers/pwm/pwm-pxa.c | 16 +---------------
>  include/linux/pwm.h   |  2 ++
>  3 files changed, 29 insertions(+), 15 deletions(-)
> 
> diff --git a/drivers/pwm/core.c b/drivers/pwm/core.c
> index 4527f09a5c50..2c6b155002a2 100644
> --- a/drivers/pwm/core.c
> +++ b/drivers/pwm/core.c
> @@ -152,6 +152,32 @@ of_pwm_xlate_with_flags(struct pwm_chip *pc, const struct of_phandle_args *args)
>  }
>  EXPORT_SYMBOL_GPL(of_pwm_xlate_with_flags);
>  
> +struct pwm_device *
> +of_pwm_single_xlate(struct pwm_chip *pc, const struct of_phandle_args *args)
> +{
> +	struct pwm_device *pwm;
> +
> +	if (pc->of_pwm_n_cells < 1)
> +		return ERR_PTR(-EINVAL);
> +
> +	/* validate that one cell is specified, optionally with flags */
> +	if (args->args_count != 1 && args->args_count != 2)
> +		return ERR_PTR(-EINVAL);
> +
> +	pwm = pwm_request_from_chip(pc, 0, NULL);
> +	if (IS_ERR(pwm))
> +		return pwm;
> +
> +	pwm->args.period = args->args[0];
> +	pwm->args.polarity = PWM_POLARITY_NORMAL;
> +
> +	if (args->args_count == 2 && args->args[2] & PWM_POLARITY_INVERTED)
> +		pwm->args.polarity = PWM_POLARITY_INVERSED;

of_pwm_xlate_with_flags is a bit more complicated. Translating
accordingly this would yield:

	if (pc->of_pwm_n_cells >= 2) {
		if (args->args_count > 1 && args->args[1] & PWM_POLARITY_INVERTED)
			pwm->args.polarity = PWM_POLARITY_INVERSED;
	}

Given that pc->of_pwm_n_cells isn't used when a phandle is parsed (in
of_pwm_get()) I think your variant is fine.

So I think technically the patch is good, for me the question is if we
want to make new drivers of_pwm_xlate_with_flags for consistency even
though this would mean that the first argument has to be 0 for all
phandles. Thierry? Lee?

Best regards
Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | https://www.pengutronix.de/ |

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