linux-kernel - Re: [PATCH v5 2/7] pwm: pca9685: Support hardware readout

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Date:   Thu, 14 Jan 2021 19:05:09 +0100
From:   Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
To:     Clemens Gruber <clemens.gruber@...ruber.com>
Cc:     Sven Van Asbroeck <thesven73@...il.com>,
        Thierry Reding <thierry.reding@...il.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-pwm@...r.kernel.org
Subject: Re: [PATCH v5 2/7] pwm: pca9685: Support hardware readout

Hello Clemens,

On Thu, Jan 14, 2021 at 06:16:22PM +0100, Clemens Gruber wrote:
> On Mon, Jan 11, 2021 at 09:35:32PM +0100, Uwe Kleine-König wrote:
> > My position here is: A consumer should disable a PWM before calling
> > pwm_put. The driver should however not enforce this and so should not
> > modify the hardware state in .free().
> > 
> > Also .probe should not change the PWM configuration.
> 
> I see. This would also allow PWMs initialized in the bootloader (e.g.
> backlights) to stay on between the bootloader and Linux and avoid
> flickering.
> 
> If no one objects, I would then no longer reset period and duty cycles
> in the driver (and for our projects, reset them in the bootloader code
> to avoid leaving PWMs on after a kernel panic and watchdog reset, etc.)
> 
> And if there is no pre-known state of the registers, we actually need
> the .get_state function fully implemented.

This sounds right.

Thanks
Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | https://www.pengutronix.de/ |

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