linux-kernel - Re: [PATCH] pwm: twl: Reliably disable TWL6030 PWMs

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Message-ID: <20160905051446.GA3532@ulmo.ba.sec>
Date:   Mon, 5 Sep 2016 07:14:46 +0200
From:   Thierry Reding <thierry.reding@...il.com>
To:     Paul Kocialkowski <contact@...lk.fr>
Cc:     linux-kernel@...r.kernel.org, linux-pwm@...r.kernel.org,
        Tony Lindgren <tony@...mide.com>, linux-omap@...r.kernel.org
Subject: Re: [PATCH] pwm: twl: Reliably disable TWL6030 PWMs

On Tue, Mar 29, 2016 at 08:55:45PM +0200, Paul Kocialkowski wrote:
> The current TWL6030 code for the TWL PWM driver does not reliably disable the
> PWM output, as tested with LEDs. The previous commit to that driver introduced
> that regression.
> 
> However, it does make sense to disable the PWM clock after resetting the PWM,
> but for some obscure reason, doing it all at once simply doesn't work.
> 
> The TWL6030 datasheet mentions that PWMs have to be disabled in two distinct
> steps. However, clearing the clock enable bit in a second step (after issuing a
> reset first) does not work.
> 
> The only approach that works is the one that was in place before the previous
> commit to the driver. It consists in enabling the PWM clock after issuing a
> reset. This is what TI kernel trees and production code seem to be using.
> 
> However, adding an extra step to disable the PWM clock seems to work reliably,
> despite looking quite odd.
> 
> Signed-off-by: Paul Kocialkowski <contact@...lk.fr>
> ---
>  drivers/pwm/pwm-twl.c | 16 ++++++++++++++++
>  1 file changed, 16 insertions(+)

Applied, thanks.

Thierry

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