linux-kernel - Re: [PATCH v2 2/6] pwm: core: make the PWM

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Message-ID: <20161006083642.6a28a629@jawa>
Date:   Thu, 6 Oct 2016 08:36:42 +0200
From:   Lukasz Majewski <l.majewski@...ess.pl>
To:     Bhuvanchandra DV <bhuvanchandra.dv@...adex.com>
Cc:     <shawnguo@...nel.org>, <thierry.reding@...il.com>,
        mark.rutland@....com, linux-pwm@...r.kernel.org,
        l.majewski@...sung.com, linux-kernel@...r.kernel.org,
        stefan@...er.ch, robh+dt@...nel.org, kernel@...gutronix.de,
        fabio.estevam@....com, linux-arm-kernel@...ts.infradead.org,
        Lothar Wassmann <LW@...O-electronics.de>
Subject: Re: [PATCH v2 2/6] pwm: core: make the PWM_POLARITY flag in DTB
 optional

Hi Bhuvanchandra,

> From: Lothar Wassmann <LW@...O-electronics.de>
> 
> Change the pwm chip driver registration, so that a chip driver that
> supports polarity inversion can still be used with DTBs that don't
> provide the 'PWM_POLARITY' flag.
> 
> This is done to provide polarity inversion support for the pwm-imx
> driver without having to modify all existing DTS files.
> 
> Signed-off-by: Lothar Wassmann <LW@...O-electronics.de>
> Signed-off-by: Bhuvanchandra DV <bhuvanchandra.dv@...adex.com>
> Suggested-by: Thierry Reding <thierry.reding@...il.com>
> ---
>  drivers/pwm/core.c | 27 ++++++++++++++++-----------
>  1 file changed, 16 insertions(+), 11 deletions(-)
> 
> diff --git a/drivers/pwm/core.c b/drivers/pwm/core.c
> index 195373e..aae8db3 100644
> --- a/drivers/pwm/core.c
> +++ b/drivers/pwm/core.c
> @@ -137,9 +137,14 @@ 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)
>  		return ERR_PTR(-EINVAL);
>  
> +	/* flags in the third cell are optional */
> +	if (args->args_count < 2)
> +		return ERR_PTR(-EINVAL);
> +
>  	if (args->args[0] >= pc->npwm)
>  		return ERR_PTR(-EINVAL);
>  
> @@ -149,10 +154,12 @@ of_pwm_xlate_with_flags(struct pwm_chip *pc,
> const struct of_phandle_args *args) 
>  	pwm->args.period = args->args[1];
>  
> -	if (args->args[2] & PWM_POLARITY_INVERTED)
> -		pwm->args.polarity = PWM_POLARITY_INVERSED;
> -	else
> -		pwm->args.polarity = PWM_POLARITY_NORMAL;
> +	if (args->args_count > 2) {
> +		if (args->args[2] & PWM_POLARITY_INVERTED)
> +			pwm_set_polarity(pwm, PWM_POLARITY_INVERSED);
			^^^^^^^^^^^^^^^^ 
			here we should set pwm->args.polarity, since
			the pwm_set_polarity() calls pwm_apply_state()
			which requires duty_cycle and period to be set.

			In this particular moment it is not yet set and
			polarity is not properly configured.

Patch fixing this will be sent as a reply to this e-mail. Please just
squash it and test on your platform.

Best regards,
Łukasz Majewski

> +		else
> +			pwm_set_polarity(pwm, PWM_POLARITY_NORMAL);
> +	}
>  
>  	return pwm;
>  }
> @@ -163,9 +170,14 @@ of_pwm_simple_xlate(struct pwm_chip *pc, const
> struct of_phandle_args *args) {
>  	struct pwm_device *pwm;
>  
> +	/* sanity check driver support */
>  	if (pc->of_pwm_n_cells < 2)
>  		return ERR_PTR(-EINVAL);
>  
> +	/* all cells are required */
> +	if (args->args_count != pc->of_pwm_n_cells)
> +		return ERR_PTR(-EINVAL);
> +
>  	if (args->args[0] >= pc->npwm)
>  		return ERR_PTR(-EINVAL);
>  
> @@ -672,13 +684,6 @@ struct pwm_device *of_pwm_get(struct device_node
> *np, const char *con_id) goto put;
>  	}
>  
> -	if (args.args_count != pc->of_pwm_n_cells) {
> -		pr_debug("%s: wrong #pwm-cells for %s\n",
> np->full_name,
> -			 args.np->full_name);
> -		pwm = ERR_PTR(-EINVAL);
> -		goto put;
> -	}
> -
>  	pwm = pc->of_xlate(pc, &args);
>  	if (IS_ERR(pwm))
>  		goto put;


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