Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.33 as permitted sender) client-ip=23.128.96.33;
Date:   Wed, 25 Oct 2023 10:53:27 +0100
From:   Sean Young <sean@mess.org>
To:     Daniel Thompson <daniel.thompson@linaro.org>
Cc:     Hans de Goede <hdegoede@redhat.com>,
        Uwe =?iso-8859-1?Q?Kleine-K=F6nig?= 
        <u.kleine-koenig@pengutronix.de>, linux-media@vger.kernel.org,
        linux-pwm@vger.kernel.org,
        Ivaylo Dimitrov <ivo.g.dimitrov.75@gmail.com>,
        Thierry Reding <thierry.reding@gmail.com>,
        Jonathan Corbet <corbet@lwn.net>,
        Jani Nikula <jani.nikula@linux.intel.com>,
        Joonas Lahtinen <joonas.lahtinen@linux.intel.com>,
        Rodrigo Vivi <rodrigo.vivi@intel.com>,
        Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>,
        David Airlie <airlied@gmail.com>,
        Daniel Vetter <daniel@ffwll.ch>,
        Javier Martinez Canillas <javierm@redhat.com>,
        Jean Delvare <jdelvare@suse.com>,
        Guenter Roeck <linux@roeck-us.net>,
        Support Opensource <support.opensource@diasemi.com>,
        Dmitry Torokhov <dmitry.torokhov@gmail.com>,
        Pavel Machek <pavel@ucw.cz>, Lee Jones <lee@kernel.org>,
        Mauro Carvalho Chehab <mchehab@kernel.org>,
        Ilpo =?iso-8859-1?Q?J=E4rvinen?= <ilpo.jarvinen@linux.intel.com>,
        Mark Gross <markgross@kernel.org>,
        Liam Girdwood <lgirdwood@gmail.com>,
        Mark Brown <broonie@kernel.org>,
        Jingoo Han <jingoohan1@gmail.com>,
        Helge Deller <deller@gmx.de>, linux-doc@vger.kernel.org,
        linux-kernel@vger.kernel.org, intel-gfx@lists.freedesktop.org,
        dri-devel@lists.freedesktop.org, linux-hwmon@vger.kernel.org,
        linux-input@vger.kernel.org, linux-leds@vger.kernel.org,
        platform-driver-x86@vger.kernel.org,
        linux-arm-kernel@lists.infradead.org, linux-fbdev@vger.kernel.org
Subject: Re: [PATCH v3 1/3] pwm: make it possible to apply pwm changes in
 atomic context
Message-ID: <ZTjll7oTNVWqygbD@gofer.mess.org>
References: <cover.1697534024.git.sean@mess.org>
 <a7fcd19938d5422abc59c968ff7b3d5c275577ed.1697534024.git.sean@mess.org>
 <90728c06-4c6c-b3d2-4723-c24711be2fa5@redhat.com>
 <20231019105118.64gdzzixwqrztjir@pengutronix.de>
 <01a505ac-320f-3819-a58d-2b82c1bf2a86@redhat.com>
 <ZTT9fvEF+lqfzGJ/@gofer.mess.org>
 <20231023133417.GE49511@aspen.lan>
MIME-Version: 1.0
Content-Type: text/plain; charset=iso-8859-1
Content-Disposition: inline
Content-Transfer-Encoding: 8bit
In-Reply-To: <20231023133417.GE49511@aspen.lan>
Precedence: bulk

On Mon, Oct 23, 2023 at 02:34:17PM +0100, Daniel Thompson wrote:
> On Sun, Oct 22, 2023 at 11:46:22AM +0100, Sean Young wrote:
> > On Sat, Oct 21, 2023 at 11:08:22AM +0200, Hans de Goede wrote:
> > > On 10/19/23 12:51, Uwe Kleine-K?nig wrote:
> > > > On Wed, Oct 18, 2023 at 03:57:48PM +0200, Hans de Goede wrote:
> > > >> On 10/17/23 11:17, Sean Young wrote:
> > > > I think it's very subjective if you consider this
> > > > churn or not.
> > >
> > > I consider it churn because I don't think adding a postfix
> > > for what is the default/expected behavior is a good idea
> > > (with GPIOs not sleeping is the expected behavior).
> > >
> > > I agree that this is very subjective and very much goes
> > > into the territory of bikeshedding. So please consider
> > > the above my 2 cents on this and lets leave it at that.
> >
> > You have a valid point. Let's focus on having descriptive function names.
> 
> For a couple of days I've been trying to resist the bikeshedding (esp.
> given the changes to backlight are tiny) so I'll try to keep it as
> brief as I can:
> 
> 1. I dislike the do_it() and do_it_cansleep() pairing. It is
>    difficult to detect when a client driver calls do_it() by mistake.
>    In fact a latent bug of this nature can only be detected by runtime
>    testing with the small number of PWMs that do not support
>    configuration from an atomic context.
> 
>    In contrast do_it() and do_it_atomic()[*] means that although
>    incorrectly calling do_it() from an atomic context can be pretty
>    catastrophic it is also trivially detected (with any PWM driver)
>    simply by running with CONFIG_DEBUG_ATOMIC_SLEEP.
> 
>    No objections (beyond churn) to fully spelt out pairings such as
>    do_it_cansleep() and do_it_atomic()[*]!

I must say I do like the look of this. Uwe, how do you feel about:
pwm_apply_cansleep() and pwm_apply_atomic()? I know we've talked about
pwm_apply_atomic in the past, however I think this this the best 
option I've seen so far.

> 2. If there is an API rename can we make sure the patch contains no
>    other changes (e.g. don't introduce any new API in the same patch).
>    Seperating renames makes the patches easier to review!
>    It makes each one smaller and easier to review!

Yes, this should have been separated out. Will fix for next version.

Thanks,

Sean