linux-kernel - Re: [PATCH v4 2/3] pwm: kona: Remove setting default smooth type and polarity for all channels

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Date:	Sun, 4 Jan 2015 17:33:06 -0800
From:	Tim Kryger <tim.kryger@...il.com>
To:	Jonathan Richardson <jonathar@...adcom.com>
Cc:	Scott Branden <sbranden@...adcom.com>,
	Arun Ramamurthy <arun.ramamurthy@...adcom.com>,
	Thierry Reding <thierry.reding@...il.com>,
	Ray Jui <rjui@...adcom.com>,
	bcm-kernel-feedback-list@...adcom.com,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	linux-pwm@...r.kernel.org
Subject: Re: [PATCH v4 2/3] pwm: kona: Remove setting default smooth type and
 polarity for all channels

On Sun, Jan 4, 2015 at 5:12 PM, Tim Kryger <tim.kryger@...il.com> wrote:
> On Tue, Dec 30, 2014 at 2:43 PM, Jonathan Richardson
> <jonathar@...adcom.com> wrote:
>> Setting the default polarity in probe to normal for all channels caused
>> the speaker pwm channel to click. The polarity does need to be set to
>> normal because the hw default is inversed whereas the pwm framework
>> defaults to normal. If a channel is enabled without setting the polarity
>> then the signal would be inversed while linux reports normal. A check
>> is now done prior to enabling the channel to ensure that the hw polarity
>> matches the desired polarity and is changed if there is a discrepency. This
>> prevents unnecessary settings being applied to unused channels but still
>> ensures the correct polarity to be set.
>
> A more direct solution that avoids the potentially undesirable
> consequences of delaying when polarity changes are written to hardware
> would be to update the PWM framework to allow for the registration of
> chips with inversed default polarity.
>
> I will post a patch for your review.

Please see:  https://lkml.org/lkml/2015/1/4/199
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