linux-kernel - Re: [PATCH 2/5] pwm: kona: Introduce Kona PWM controller support

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Message-ID: <CAAYSxhqquF87NEJj8n3M7E8LWNgQGQdTqQmHPX9sdmvtBiSBTA@mail.gmail.com>
Date:	Tue, 26 Nov 2013 13:32:13 -0800
From:	Tim Kryger <tim.kryger@...aro.org>
To:	Thierry Reding <thierry.reding@...il.com>
Cc:	Rob Herring <rob.herring@...xeda.com>,
	Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Stephen Warren <swarren@...dotorg.org>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Rob Landley <rob@...dley.net>,
	Christian Daudt <bcm@...thebug.org>,
	Grant Likely <grant.likely@...aro.org>,
	Linux PWM List <linux-pwm@...r.kernel.org>,
	Device Tree List <devicetree@...r.kernel.org>,
	Linux Doc List <linux-doc@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Broadcom Kernel Feedback List 
	<bcm-kernel-feedback-list@...adcom.com>,
	Linux ARM Kernel List <linux-arm-kernel@...ts.infradead.org>,
	Linaro Patches List <patches@...aro.org>
Subject: Re: [PATCH 2/5] pwm: kona: Introduce Kona PWM controller support

On Tue, Nov 26, 2013 at 1:45 AM, Thierry Reding
<thierry.reding@...il.com> wrote:
> On Mon, Nov 25, 2013 at 05:38:44PM -0800, Tim Kryger wrote:

> Okay, that's fine then. Do you have a pointer to that documentation?

Unfortunately the documentation is not publicly available at the moment.

>> The hardware is always enabled and at best can be be configured to
>> operate at zero duty.
>
> What good are the PWMOUT_ENABLE bits then? Is that really only used for
> triggering updates? That's what another comment suggests, but if so, can
> the comment in kona_pwmc_apply_settings() be extended to mention that?

The guidance from the documentation is to treat the enable bits as a trigger.

Sure I can expand the comment to try and make this more clear.

>> The settings in HW may have already been triggered and might not be
>> what you want.
>>
>> For example:
>>
>> /sys/class/pwm/pwmchip0/pwm1# echo 1 > enable
>> /sys/class/pwm/pwmchip0/pwm1# echo 5000 > period
>> /sys/class/pwm/pwmchip0/pwm1# echo 2000 > duty_cycle
>> /sys/class/pwm/pwmchip0/pwm1# echo 0 > enable
>> /sys/class/pwm/pwmchip0/pwm1# echo 1 > enable
>
> I'm not exactly sure what this is supposed to demonstrate.

The computation has to be performed for every operation except the disable.

> All of that said, I wasn't able to dig up a normative policy and either
> of your proposed alternatives do exist in the kernel, so I withdraw any
> objections regarding MODULE_AUTHOR. Take your pick.

Thanks
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