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

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Date:   Tue, 25 Oct 2016 08:58:49 +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,

> Hi Lukasz,
> 
> On Mon, 24 Oct 2016 23:14:58 +0200
> Lukasz Majewski <l.majewski@...ess.pl> wrote:
> 
> > 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.
> 
> It's really simple to make this series bisectable, all you have to do
> is move patch 6 before patch 5.

Hmm... You are right, I do wonder why I didn't get this idea from the
very beginning.

> This being said, I really think you
> should follow Stefan's recommendation: base your changes on mainline
> and switch to the atomic hook before supporting polarity setting.

I will do my best :-)

Best regards,

Łukasz Majewski

> 
> Regards,
> 
> Boris


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