From: Andy Shevchenko <andy.shevchenko@gmail.com>
To: "Uwe Kleine-König" <u.kleine-koenig@pengutronix.de>
Cc: Thierry Reding <thierry.reding@gmail.com>,
Clemens Gruber <clemens.gruber@pqgruber.com>,
Sven Van Asbroeck <thesven73@gmail.com>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
"linux-pwm@vger.kernel.org" <linux-pwm@vger.kernel.org>
Subject: Re: [PATCH v5 2/7] pwm: pca9685: Support hardware readout
Date: Mon, 22 Mar 2021 14:15:08 +0200 [thread overview]
Message-ID: <CAHp75Vc6YnHJdt0HhV9AZtpLHLapHZb08O5ygg++PX+u04m--A@mail.gmail.com> (raw)
In-Reply-To: <20210322114826.ahwhbqxjxfg3nmrf@pengutronix.de>
On Mon, Mar 22, 2021 at 1:48 PM Uwe Kleine-König
<u.kleine-koenig@pengutronix.de> wrote:
> On Mon, Mar 22, 2021 at 01:40:57PM +0200, Andy Shevchenko wrote:
> > On Mon, Mar 22, 2021 at 1:22 PM Uwe Kleine-König
> > <u.kleine-koenig@pengutronix.de> wrote:
> > > On Mon, Mar 22, 2021 at 11:38:40AM +0200, Andy Shevchenko wrote:
> > > > On Monday, March 22, 2021, Thierry Reding <thierry.reding@gmail.com> wrote:
> > > > > On Fri, Jan 29, 2021 at 09:37:47PM +0100, Clemens Gruber wrote:
> > > > > > Thierry: Would you accept it if we continue to reset the registers in
> > > > > > .probe?
> > > > >
> > > > > Yes, I think it's fine to continue to reset the registers since that's
> > > > > basically what the driver already does. It'd be great if you could
> > > > > follow up with a patch that removes the reset and leaves the hardware in
> > > > > whatever state the bootloader has set up. Then we can take that patch
> > > > > for a ride and see if there are any complains about it breaking. If
> > > > > there are we can always try to fix them, but as a last resort we can
> > > > > also revert, which then may be something we have to live with. But I
> > > > > think we should at least try to make this consistent with how other
> > > > > drivers do this so that people don't stumble over this particular
> > > > > driver's
> > > >
> > > > I guess we may miss (a PCB / silicon design flaw or warm boot case) when
> > > > boot loader left device completely untouched and device either in wrong
> > > > state because if failed reset (saw this on PCA9555 which has a
> > > > corresponding errata), or simply we have done a warm reset of the system.
> > > > So, we also have to understand how to properly exit.
> > >
> > > I don't think that not resetting is a real problem. My argumentation
> > > goes as follows:
> > >
> > > When the PWM driver is loaded and the PWM configuration is invalid, it
> > > was already invalid for the time between power up (or warm start) and
> > > PWM driver load time. Then it doesn't really hurt to keep the PWM
> > > in this invalid state for a little moment longer until the consumer of
> > > the PWM becomes active.
> >
> > But this won't work in the cases when we have a chip with a shared
> > settings for period and/or duty cycle. You will never have a user come
> > due to -EBUSY.
>
> That's wrong, the first consumer to enable the PWM (in software) is
> supposed to be able to change the settings.
If it's a critical PWM, how can you be allowed to do that?
And if so, what is the difference between resetting the device in this
case? You may consider it as a change to the settings by the first
consumer.
--
With Best Regards,
Andy Shevchenko
next prev parent reply other threads:[~2021-03-22 12:16 UTC|newest]
Thread overview: 36+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20201216125320.5277-1-clemens.gruber@pqgruber.com>
[not found] ` <20201216125320.5277-2-clemens.gruber@pqgruber.com>
2020-12-17 4:00 ` [PATCH v5 2/7] pwm: pca9685: Support hardware readout Sven Van Asbroeck
2020-12-17 17:43 ` Clemens Gruber
2020-12-17 17:52 ` Sven Van Asbroeck
2021-01-03 17:04 ` Clemens Gruber
2021-01-07 14:18 ` Sven Van Asbroeck
2021-01-11 20:43 ` Uwe Kleine-König
2021-03-22 8:34 ` Thierry Reding
2021-03-31 10:25 ` Uwe Kleine-König
2021-03-31 15:52 ` Thierry Reding
2021-04-06 6:33 ` Uwe Kleine-König
2021-04-06 13:47 ` Thierry Reding
2021-04-06 20:44 ` Uwe Kleine-König
2021-03-22 8:15 ` Thierry Reding
2021-01-11 20:35 ` Uwe Kleine-König
2021-01-14 17:16 ` Clemens Gruber
2021-01-14 18:05 ` Uwe Kleine-König
2021-03-22 8:53 ` Thierry Reding
[not found] ` <CAGngYiW=KhCOZX3tPMFykXzpWLpj3qusN2OXVPSfHLRcyts+wA@mail.gmail.com>
2021-01-29 16:31 ` Clemens Gruber
2021-01-29 18:05 ` Sven Van Asbroeck
2021-01-29 20:37 ` Clemens Gruber
2021-01-29 21:24 ` Sven Van Asbroeck
2021-01-29 22:16 ` Sven Van Asbroeck
2021-02-01 17:24 ` Clemens Gruber
2021-03-01 21:52 ` Uwe Kleine-König
2021-03-04 13:22 ` Clemens Gruber
2021-02-14 14:46 ` Clemens Gruber
2021-03-22 9:19 ` Thierry Reding
[not found] ` <CAHp75Ve2FFEMsAv8S18bUDFsH2UkiQ5UvgcRtZ=j30syQtEirw@mail.gmail.com>
2021-03-22 11:22 ` Uwe Kleine-König
2021-03-22 11:40 ` Andy Shevchenko
2021-03-22 11:48 ` Uwe Kleine-König
2021-03-22 12:15 ` Andy Shevchenko [this message]
2021-03-22 13:25 ` Uwe Kleine-König
2021-03-27 16:05 ` Clemens Gruber
2021-03-22 9:14 ` Thierry Reding
2021-03-22 8:47 ` Thierry Reding
2020-12-15 21:22 [PATCH v5 1/7] pwm: pca9685: Switch to atomic API Clemens Gruber
2020-12-15 21:22 ` [PATCH v5 2/7] pwm: pca9685: Support hardware readout Clemens Gruber
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