linux-kernel - Re: [PATCH v4 1/4] pwm: pca9685: Switch to atomic API

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Date:   Fri, 11 Dec 2020 09:33:55 +0100
From:   Thierry Reding <thierry.reding@...il.com>
To:     Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
Cc:     Sven Van Asbroeck <thesven73@...il.com>,
        Clemens Gruber <clemens.gruber@...ruber.com>,
        linux-pwm@...r.kernel.org, Lee Jones <lee.jones@...aro.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Mika Westerberg <mika.westerberg@...ux.intel.com>,
        David Jander <david@...tonic.nl>
Subject: Re: [PATCH v4 1/4] pwm: pca9685: Switch to atomic API

On Thu, Dec 10, 2020 at 09:39:26PM +0100, Uwe Kleine-König wrote:
> Hello Thierry,
> 
> On Thu, Dec 10, 2020 at 06:10:45PM +0100, Thierry Reding wrote:
> > Like I said, that's not what I was saying. I was merely saying that if
> > there aren't any use-cases that current users rely on that would be
> > broken by using this simpler implementation, then I'm okay with it, even
> > if it's less flexible than a more complicated implementation. It should
> > be possible to determine what the current users are by inspecting device
> > trees present in the kernel. Anything outside the kernel isn't something
> > we need to consider, as usual.
> 
> If "users in mainline" is the criteria that's a word.

I didn't say "users in mainline", I said "use-cases". What I don't want
to happen is for this change under discussion to break any existing use-
cases of any existing users in the kernel. I said that we can determine
what the existing users are by looking at which device trees use the
compatible strings that the driver matches on.

> So you agree we remove the following drivers?:
> 
>  - pwm-hibvt.c
>    Last driver specific change in Feb 2019, no mainline user
>  - pwm-sprd.c
>    Last driver specific change in Aug 2019, no mainline user

No, that's an extrapolation of what I was saying above. Drivers with no
apparent users are a separate topic, so don't conflate it with the issue
at hand.

While it's certainly unfortunate that these don't seem to be used, I see
no reason why we should remove them. They don't create much of a
maintenance burden, so I'm fine with keeping them in the hopes that
users may still show up at some point.

> Most PWMs are added to cpu.dtsi files with status = "disabled", I wonder
> if it makes sense to check the machine.dts files if some of the PMWs are
> completely unused. Do you consider status = "okay" a use that we have to
> retain even if the node has no phandle?

A PWM controller may be in use via sysfs even if it has no phandle.

Thierry

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