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From: Clemens Gruber <clemens.gruber@pqgruber.com>
To: Matthias Schiffer <matthias.schiffer@ew.tq-group.com>
Cc: "Uwe Kleine-König" <u.kleine-koenig@pengutronix.de>,
	thierry.reding@gmail.com, linux-pwm@vger.kernel.org,
	linux-kernel@vger.kernel.org, andy.shevchenko@gmail.com
Subject: Re: (EXT) Re: [PATCH 1/4] pwm: pca9685: remove unused duty_cycle struct element
Date: Mon, 30 Mar 2020 17:12:31 +0200	[thread overview]
Message-ID: <20200330151231.GA1650@workstation.tuxnet> (raw)
In-Reply-To: <32ec35c2b3da119dd2c7bc09742796a0d8a9607e.camel@ew.tq-group.com>

Hi,

On Wed, Feb 26, 2020 at 06:03:02PM +0100, Matthias Schiffer wrote:
> As it turns out, this driver is broken in yet another way I didn't find
> before: For changing the global prescaler the chip needs to be put into
> sleep mode, but the driver doesn't follow the restart sequence
> described in the datasheet when waking it back up. In consequence,
> changing the period of one PWM does not only modify the period of all
> PWMs (which is bad enough, but can't be avoided with this hardware),
> but it also leaves all PWMs disabled...

I am unable to reproduce this: If I set a specific duty cycle on a
channel and then change the period, the channel stays active.
I can see the brightness of an LED decrease if I increase the period.

This is expected, because after the SLEEP bit is set, we wait for
500usecs and then write to the LED ON/OFF registers.
This leaves the channel enabled with the new period (but with old
duty_ns value => different ratio)

A few years ago, I played around with the idea of remembering the
duty_ns to period_ns ratio and setting it accordingly after a period
change, possibly also with a shortcut of setting the RESTART bit if the
ratio did not change. Maybe after the switch to the atomic API, this
would be a nice improvement.

Best regards,
Clemens

  parent reply	other threads:[~2020-03-30 15:12 UTC|newest]

Thread overview: 39+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-02-26 13:52 [PATCH 1/4] pwm: pca9685: remove unused duty_cycle struct element Matthias Schiffer
2020-02-26 13:52 ` [PATCH 2/4] pwm: pca9685: remove ALL_LED PWM channel Matthias Schiffer
2020-03-30 13:07   ` Thierry Reding
2020-03-30 13:15     ` Thierry Reding
2020-03-30 13:19     ` Andy Shevchenko
2020-03-30 15:38       ` Thierry Reding
2020-03-30 13:34     ` Clemens Gruber
2020-03-30 15:40       ` Thierry Reding
2020-03-30 15:43         ` Thierry Reding
2020-03-30 16:07         ` Clemens Gruber
2020-03-31 12:09           ` (EXT) " Matthias Schiffer
2020-03-31 13:14             ` Clemens Gruber
2020-02-26 13:52 ` [PATCH 3/4] pwm: pca9685: initialize all LED registers during probe Matthias Schiffer
2020-02-26 15:00   ` Uwe Kleine-König
2020-02-26 16:13     ` (EXT) " Matthias Schiffer
2020-03-30 13:07       ` Thierry Reding
2020-02-26 13:52 ` [PATCH 4/4] pwm: pca9685: migrate config/enable/disable to apply Matthias Schiffer
2020-02-26 15:05   ` Uwe Kleine-König
2020-02-26 15:10 ` [PATCH 1/4] pwm: pca9685: remove unused duty_cycle struct element Uwe Kleine-König
2020-02-26 17:03   ` (EXT) " Matthias Schiffer
2020-02-26 19:21     ` Uwe Kleine-König
2020-02-28 13:26       ` (EXT) " Matthias Schiffer
2020-03-30 15:12     ` Clemens Gruber [this message]
2020-04-03 23:50       ` Sven Van Asbroeck
2020-04-04 17:35         ` Clemens Gruber
2020-04-04 20:17           ` Sven Van Asbroeck
2020-04-06  9:51             ` Thierry Reding
2020-04-07 13:00               ` (EXT) " Matthias Schiffer
2020-04-09 11:42               ` Sven Van Asbroeck
2020-04-03 23:47     ` Sven Van Asbroeck
2020-04-07 14:46       ` (EXT) " Matthias Schiffer
2020-04-08  8:00         ` Matthias Schiffer
2020-03-30 13:07 ` Thierry Reding
2020-03-30 13:18   ` Andy Shevchenko
2020-03-30 16:02     ` Thierry Reding
2020-03-30 16:10       ` Clemens Gruber
2020-04-01 16:36       ` Clemens Gruber
2020-04-01 17:45         ` Thierry Reding
2020-04-02  7:10           ` (EXT) " Matthias Schiffer

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