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Date: Fri, 9 Nov 2012 10:59:31 +0000
From: "Philip, Avinash" <avinashphilip@...com>
To: Thierry Reding <thierry.reding@...onic-design.de>
CC: "grant.likely@...retlab.ca" <grant.likely@...retlab.ca>,
"rob.herring@...xeda.com" <rob.herring@...xeda.com>,
"rob@...dley.net" <rob@...dley.net>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"devicetree-discuss@...ts.ozlabs.org"
<devicetree-discuss@...ts.ozlabs.org>,
"linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
"Nori, Sekhar" <nsekhar@...com>,
"Hebbar, Gururaja" <gururaja.hebbar@...com>
Subject: RE: [PATCH] pwm: Device tree support for PWM polarity.
On Fri, Nov 09, 2012 at 14:00:28, Thierry Reding wrote:
> On Mon, Oct 29, 2012 at 11:10:27PM +0530, Philip, Avinash wrote:
> > From: "Philip, Avinash" <avinashphilip@...com>
> >
> > Adds support for 3rd cell in pwm-specifier. PWM polarity is encoded in
> > device tree support in bit encoded form. Platforms require polarity of
> > PWM device initialized during PWM device initialization has to encode
> > polarity in 3rd cell of pwm-specifier.
> >
> > Signed-off-by: Philip, Avinash <avinashphilip@...com>
> > ---
> > :100644 100644 73ec962... e522c59... M Documentation/devicetree/bindings/pwm/pwm.txt
> > :100644 100644 f5acdaa... 1c6d50b... M drivers/pwm/core.c
> > :100644 100644 112b314... d77c5b3... M include/linux/pwm.h
> > Documentation/devicetree/bindings/pwm/pwm.txt | 22 +++++++++++++++++++---
> > drivers/pwm/core.c | 13 ++++++++++++-
> > include/linux/pwm.h | 7 +++++++
> > 3 files changed, 38 insertions(+), 4 deletions(-)
> >
> > diff --git a/Documentation/devicetree/bindings/pwm/pwm.txt b/Documentation/devicetree/bindings/pwm/pwm.txt
> > index 73ec962..e522c59 100644
> > --- a/Documentation/devicetree/bindings/pwm/pwm.txt
> > +++ b/Documentation/devicetree/bindings/pwm/pwm.txt
> > @@ -37,10 +37,26 @@ device:
> > pwm-names = "backlight";
> > };
> >
> > +Note that in the example above, specifying the "pwm-names" is redundant
> > +because the name "backlight" would be used as fallback anyway.
> > +
> > pwm-specifier typically encodes the chip-relative PWM number and the PWM
> > -period in nanoseconds. Note that in the example above, specifying the
> > -"pwm-names" is redundant because the name "backlight" would be used as
> > -fallback anyway.
> > +period in nanoseconds.
>
> Can you separate this by a blank line, please?
Ok
>
> > +Optional pwm-specifier can be encoded in 3rd cell in bit encoded form.
> > + -------------------------------------------------------------
> > +| Property | BIT position | Encoding |
> > +|-------------------------------------------------------------|
> > +| Polarity | 0 | Set -> Polarity inversed |
> > +| | | Clear -> Polarity Normal |
> > + -------------------------------------------------------------
> > +
>
> Using this kind of table isn't very common in device tree documentation
> and the description above the table is a little vague. Maybe something
> like this would be more explicit:
>
> ---[snip]---
>
> Optionally, the pwm-specifier can encode a number of flags in a third
> cell:
> - bit 0: PWM signal polarity (0: normal polarity, 1: inverse polarity)
>
> ---[snip]---
>
> > +Exapmple with optional PWM specifier for inversed polarity
>
> "Example"
Ok I will correct it.
>
> > +
> > + bl: backlight {
> > + pwms = <&pwm 0 5000000 1>;
> > + pwm-names = "backlight";
> > + };
> > +
> >
> > 2) PWM controller nodes
> > -----------------------
> > diff --git a/drivers/pwm/core.c b/drivers/pwm/core.c
> > index f5acdaa..1c6d50b 100644
> > --- a/drivers/pwm/core.c
> > +++ b/drivers/pwm/core.c
> > @@ -146,6 +146,15 @@ of_pwm_simple_xlate(struct pwm_chip *pc, const struct of_phandle_args *args)
> >
> > pwm_set_period(pwm, args->args[1]);
> >
> > + if (pc->of_pwm_n_cells > 2) {
> > + enum pwm_polarity polarity;
> > +
> > + /* Initialize polarity of PWM device */
> > + polarity = args->args[2] & POLARITY_BIT ?
> > + PWM_POLARITY_INVERSED : PWM_POLARITY_NORMAL;
>
> Can we rewrite this as:
>
> if (args->args[2] & POLARITY_BIT)
> pwm_set_polarity(pwm, PWM_POLARITY_INVERSED);
> else
> pwm_set_polarity(pwm, PWM_POLARITY_NORMAL);
>
> ?
Ok
>
> > + pwm_set_polarity(pwm, polarity);
> > + }
> > +
> > return pwm;
> > }
> >
> > @@ -156,7 +165,9 @@ static void of_pwmchip_add(struct pwm_chip *chip)
> >
> > if (!chip->of_xlate) {
> > chip->of_xlate = of_pwm_simple_xlate;
> > - chip->of_pwm_n_cells = 2;
> > +
> > + if (chip->of_pwm_n_cells != 3)
> > + chip->of_pwm_n_cells = 2;
> > }
>
> I don't like the implicitness in this code. I think we should make this
> more explicit for driver writers, so that if .of_xlate is set to NULL,
> the default of_pwm_simple_xlate() is used. For all other cases we should
> export of_pwm_xlate_with_flags(), so that the driver can explicitly set
> the .of_xlate field to that function.
>
> That will of course imply that the extra code that you added to
> of_pwm_simple_xlate() is moved into a separate function.
Ok I will go for export of_pwm_xlate_with_flags().
>
> >
> > of_node_get(chip->dev->of_node);
> > diff --git a/include/linux/pwm.h b/include/linux/pwm.h
> > index 112b314..d77c5b3 100644
> > --- a/include/linux/pwm.h
> > +++ b/include/linux/pwm.h
> > @@ -78,6 +78,13 @@ enum {
> > PWMF_ENABLED = 1 << 1,
> > };
> >
> > +/*
> > + * DT Platform property support.
> > + * POLARITY - set bit 0 in DT platform property
> > + */
> > +
> > +#define POLARITY_BIT BIT(0)
> > +
>
> This doesn't belong in a public header. It should be defined in the
> core.c source file. Maybe rename it to something like PWM_SPEC_POLARITY
> to make it more obvious that it defines a bit in the PWM specifier. You
> can reduce the comment to a single line, because the second doesn't add
> any additional information. Something like this:
>
> /* flags in the third cell of the DT PWM specifier */
> #define PWM_SPEC_POLARITY (1 << 0)
Ok
Thanks
Avinash
>
> Thierry
>
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