linux-kernel - Re: [PATCH 6/6] pwm: imx: Introduce "polarity

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Date:   Mon, 24 Oct 2016 23:14:58 +0200
From:   Lukasz Majewski <l.majewski@...ess.pl>
To:     Boris Brezillon <boris.brezillon@...e-electrons.com>
Cc:     Thierry Reding <thierry.reding@...il.com>,
        Stefan Agner <stefan@...er.ch>, linux-pwm@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Fabio Estevam <fabio.estevam@....com>,
        Fabio Estevam <festevam@...il.com>,
        Lothar Wassmann <LW@...o-electronics.de>,
        Bhuvanchandra DV <bhuvanchandra.dv@...adex.com>,
        kernel@...gutronix.de
Subject: Re: [PATCH 6/6] pwm: imx: Introduce "polarity_supported" flag to
 PWMv2 driver

Hi Boris,

> On Mon, 24 Oct 2016 17:28:52 +0200
> Boris Brezillon <boris.brezillon@...e-electrons.com> wrote:
> 
> > On Sun, 23 Oct 2016 23:45:46 +0200
> > Lukasz Majewski <l.majewski@...ess.pl> wrote:
> > 
> > > The need for set_polarity() function has been removed by
> > > implementing PWM atomic support (apply() callback).
> > > 
> > > To indicate that the PWMv2 supports polarity inversion, new flag -
> > > "polarity_supported" has been introduced.
> > > 
> > > Signed-off-by: Lukasz Majewski <l.majewski@...ess.pl>
> > > ---
> > >  drivers/pwm/pwm-imx.c | 4 +++-
> > >  1 file changed, 3 insertions(+), 1 deletion(-)
> > > 
> > > diff --git a/drivers/pwm/pwm-imx.c b/drivers/pwm/pwm-imx.c
> > > index 02d3dfd..be3034d 100644
> > > --- a/drivers/pwm/pwm-imx.c
> > > +++ b/drivers/pwm/pwm-imx.c
> > > @@ -258,6 +258,7 @@ static struct pwm_ops imx_pwm_ops_v2 = {
> > >  };
> > >  
> > >  struct imx_pwm_data {
> > > +	bool polarity_supported;
> > >  	struct pwm_ops *pwm_ops;
> > >  };
> > >  
> > > @@ -266,6 +267,7 @@ static struct imx_pwm_data imx_pwm_data_v1 = {
> > >  };
> > >  
> > >  static struct imx_pwm_data imx_pwm_data_v2 = {
> > > +	.polarity_supported = true,
> > >  	.pwm_ops = &imx_pwm_ops_v2,
> > >  };
> > >  
> > > @@ -313,7 +315,7 @@ static int imx_pwm_probe(struct
> > > platform_device *pdev) imx->chip.base = -1;
> > >  	imx->chip.npwm = 1;
> > >  	imx->chip.can_sleep = true;
> > > -	if (data->pwm_ops->set_polarity) {
> > > +	if (data->polarity_supported) {  
> > 
> > You're still breaking backward compatibility with DTs defining
> > #pwm-cells = 2.
> > 
> > Please test the #pwm-cells value before deciding which of_xlate
> > should be used.
> 
> Nevermind, I didn't look at [1] and [2].

Yes, some patches are required to make this code work. Especially, I
wanted to explicitly reuse and credit work already done by
Bhuvanchandra.

> But still, your series is not bisectable: this change should be part
> of patch 5 where you remove the ->set_polarity implementation.
> Otherwise, this means you don't support polarity setting between
> patch 5 and 6.

Frankly speaking, I did it on purpose, to have operations in commits
logically separated.

I personally, do detest commits which blur the picture and are not
corresponding to one single logical change - for example remove some
large chunk of code and also add some tiny, new flag.

For me it is not a problem to have polarity disabled between patches 5
and 6, since at the end of the day we have it enabled.

Thanks for your support and review,

Best regards,

Łukasz Majewski

> 
> > 
> > >  		dev_dbg(&pdev->dev, "PWM supports output
> > > inversion\n"); imx->chip.of_xlate = of_pwm_xlate_with_flags;
> > >  		imx->chip.of_pwm_n_cells = 3;  
> > 
> 
> [1]http://patchwork.ozlabs.org/patch/679706/
> [2]http://patchwork.ozlabs.org/patch/679707/


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