linux-kernel - Re: [PATCH v3 3/7] PWM: add pwm-stm32 DT bindings

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Message-ID: <20161205083535.GB14004@dell>
Date:   Mon, 5 Dec 2016 08:35:35 +0000
From:   Lee Jones <lee.jones@...aro.org>
To:     Thierry Reding <thierry.reding@...il.com>
Cc:     Benjamin Gaignard <benjamin.gaignard@...aro.org>,
        robh+dt@...nel.org, mark.rutland@....com, alexandre.torgue@...com,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-pwm@...r.kernel.org, jic23@...nel.org, knaack.h@....de,
        lars@...afoo.de, pmeerw@...erw.net, linux-iio@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, fabrice.gasnier@...com,
        gerald.baeza@...com, arnaud.pouliquen@...com,
        linus.walleij@...aro.org, linaro-kernel@...ts.linaro.org,
        Benjamin Gaignard <benjamin.gaignard@...com>
Subject: Re: [PATCH v3 3/7] PWM: add pwm-stm32 DT bindings

On Mon, 05 Dec 2016, Thierry Reding wrote:

> On Fri, Dec 02, 2016 at 11:17:18AM +0100, Benjamin Gaignard wrote:
> > Define bindings for pwm-stm32
> > 
> > version 2:
> > - use parameters instead of compatible of handle the hardware configuration
> > 
> > Signed-off-by: Benjamin Gaignard <benjamin.gaignard@...com>
> > ---
> >  .../devicetree/bindings/pwm/pwm-stm32.txt          | 38 ++++++++++++++++++++++
> >  1 file changed, 38 insertions(+)
> >  create mode 100644 Documentation/devicetree/bindings/pwm/pwm-stm32.txt
> > 
> > diff --git a/Documentation/devicetree/bindings/pwm/pwm-stm32.txt b/Documentation/devicetree/bindings/pwm/pwm-stm32.txt
> > new file mode 100644
> > index 0000000..575b9fb
> > --- /dev/null
> > +++ b/Documentation/devicetree/bindings/pwm/pwm-stm32.txt
> > @@ -0,0 +1,38 @@
> > +STMicroelectronics PWM driver bindings for STM32
> 
> Technically this bindings describe devices, so "driver binding" is a
> somewhat odd wording. Perhaps:
> 
> 	STMicroelectronics STM32 General Purpose Timer PWM bindings
> 
> ?
> 
> > +
> > +Must be a sub-node of STM32 general purpose timer driver
> > +Parent node properties are describe in ../mfd/stm32-general-purpose-timer.txt
> 
> Again, "driver parent node" is odd. Perhaps:
> 
> 	Must be a sub-node of an STM32 General Purpose Timer device tree
> 	node. See ../mfd/stm32-general-purpose-timer.txt for details about
> 	the parent node.
> 
> ?
> 
> > +Required parameters:
> > +- compatible:		Must be "st,stm32-pwm"
> > +- pinctrl-names: 	Set to "default".
> > +- pinctrl-0: 		List of phandles pointing to pin configuration nodes
> > +			for PWM module.
> > +			For Pinctrl properties, please refer to [1].
> 
> Your indentation and capitalization are inconsistent. Also, please refer
> to the pinctrl bindings by relative path and inline, rather than as a
> footnote reference.
> 
> > +
> > +Optional parameters:
> > +- st,breakinput:	Set if the hardware have break input capabilities
> > +- st,breakinput-polarity: Set break input polarity. Default is 0
> > +			 The value define the active polarity:
> > +			  - 0 (active LOW)
> > +			  - 1 (active HIGH)
> 
> Could we fold these into a single property? If st,breakinput-polarity is
> not present it could simply mean that there is no break input, and if it
> is present you don't have to rely on a default.
> 
> > +- st,pwm-num-chan:	Number of available PWM channels.  Default is 0.
> 
> The pwm- prefix is rather redundant since the node is already named pwm.
> Why not simply st,channels? Or simply channels, since it's not really
> anything specific to this hardware.
> 
> Come to think of it, might be worth having a discussion with our DT
> gurus about what their stance is on using the # as prefix for numbers
> (such as in #address-cells or #size-cells). This could be #channels to
> mark it more explicitly as representing a count.

Unfortunately that ship has sailed.

st,pwm-num-chan already exists (with your blessing).  It's usually
suggested to reuse exiting properties when writing new bindings.

> > +- st,32bits-counter:	Set if the hardware have a 32 bits counter
> > +- st,complementary:	Set if the hardware have complementary output channels
> 
> "hardware has" and also maybe mention explicitly that this is a boolean
> property. Otherwise people might be left wondering what it should be set
> to. Or maybe word this differently to imply that it's boolean:
> 
> 	- st,32bits-counter: if present, the hardware has a 32 bit counter
> 	- st,complementary: if present, the hardware has a complementary
> 	                    output channel
> 
> Thierry



-- 
Lee Jones
Linaro STMicroelectronics Landing Team Lead
Linaro.org │ Open source software for ARM SoCs
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