Re: [PATCH v2 10/16] pwm: Add PWM modes

From: Rob Herring <robh@kernel.org>
To: Claudiu Beznea <Claudiu.Beznea@microchip.com>
Cc: Thierry Reding <thierry.reding@gmail.com>,
	Mark Rutland <mark.rutland@arm.com>,
	Russell King <linux@armlinux.org.uk>,
	Daniel Mack <daniel@zonque.org>,
	Haojian Zhuang <haojian.zhuang@gmail.com>,
	Robert Jarzmik <robert.jarzmik@free.fr>,
	Jonathan Corbet <corbet@lwn.net>,
	Nicolas Ferre <nicolas.ferre@microchip.com>,
	Alexandre Belloni <alexandre.belloni@free-electrons.com>,
	Linux PWM List <linux-pwm@vger.kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"moderated list:ARM/FREESCALE IMX / MXC ARM ARCHITECTURE"
	<linux-arm-kernel@lists.infradead.org>,
	linux-amlogic@lists.infradead.org,
	"open list:ARM/Rockchip SoC..."
	<linux-rockchip@lists.infradead.org>,
	"moderated list:BROADCOM BCM2835 ARM ARCHITECTURE"
	<linux-rpi-kernel@lists.infradead.org>,
	"open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS"
	<devicetree@vger.kernel.org>
Subject: Re: [PATCH v2 10/16] pwm: Add PWM modes
Date: Mon, 22 Jan 2018 12:12:44 -0600	[thread overview]
Message-ID: <CAL_JsqJho2OrdnHwRPpYsbNB4RFTq5qSLA=36D2zy=Mi7B8XwQ@mail.gmail.com> (raw)
In-Reply-To: <c5aeb8df-6aa8-cde4-9305-08777cac2f45@microchip.com>

On Mon, Jan 22, 2018 at 2:54 AM, Claudiu Beznea
<Claudiu.Beznea@microchip.com> wrote:
>
>
> On 20.01.2018 00:34, Rob Herring wrote:
>> On Fri, Jan 12, 2018 at 04:22:57PM +0200, Claudiu Beznea wrote:
>>> Define a macros for PWM modes to be used by device tree sources.
>>>
>>> Signed-off-by: Claudiu Beznea <claudiu.beznea@microchip.com>
>>> ---
>>>  include/dt-bindings/pwm/pwm.h | 3 +++
>>>  1 file changed, 3 insertions(+)
>>>
>>> diff --git a/include/dt-bindings/pwm/pwm.h b/include/dt-bindings/pwm/pwm.h
>>> index ab9a077e3c7d..b8617431f8ec 100644
>>> --- a/include/dt-bindings/pwm/pwm.h
>>> +++ b/include/dt-bindings/pwm/pwm.h
>>> @@ -12,4 +12,7 @@
>>>
>>>  #define PWM_POLARITY_INVERTED                       (1 << 0)
>>>
>>> +#define PWM_DTMODE_NORMAL                   (1 << 0)
>>
>> Bit 0 is already taken. I think you mean (0 << 1)?
> I wanted to have the PWM modes in a new cell, so that the pwms binding to be
> something like:
> pwms=<pwm-controller pwm-channel pwm-period pwm-flags pwm-mode>
>
> If you think it is mode feasible to also include PWM mode in the cell for
> PWM flags, please let me know.

Yes, but you have to make "normal" be no bit set to be compatible with
everything already out there.

>> Personally, I'd just drop this define. A define for a 0 value makes more
>> sense when each state is equally used (like active high or low), but if
>> 0 is the more common case, then I don't the need for a define.
> I want it to have these defines like bit defines:
> PWM_DTMODE_NORMAL=0x1
> PWM_DTMODE_COMPLEMENTARY=0x2
> PWM_DTMODE_PUSH_PULL=0x4

Thinking about this some more, shouldn't the new modes just be
implied? A client is going to require one of these modes or it won't
work right.

Also complementary mode could be accomplished with a single pwm output
and a board level inverter, right? How would that be handled when the
PWM driver doesn't support that mode?

Rob