linux-kernel - Re: About clk maintainership [Was: Re: [PULL] Add variants of devm_clk_get for prepared and enabled clocks enabled clocks]

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Message-ID: <20210731120004.i3affxw7upl5y4c5@pengutronix.de>
Date:   Sat, 31 Jul 2021 14:00:04 +0200
From:   Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
To:     Stephen Boyd <sboyd@...nel.org>,
        Russell King <linux@...linux.org.uk>
Cc:     alexandre.belloni@...tlin.com,
        Michael Turquette <mturquette@...libre.com>,
        thierry.reding@...il.com, lee.jones@...aro.org,
        linux-clk@...r.kernel.org, linux-rtc@...r.kernel.org,
        Ludovic.Desroches@...rochip.com, o.rempel@...gutronix.de,
        andy.shevchenko@...il.com, aardelean@...iqon.com,
        linux-pwm@...r.kernel.org, Arnd Bergmann <arnd@...db.de>,
        broonie@...nel.org, Jonathan.Cameron@...wei.com,
        linux-arm-kernel@...ts.infradead.org, a.zummo@...ertech.it,
        linux-kernel@...r.kernel.org, linux-spi@...r.kernel.org,
        wsa@...nel.org, kernel@...gutronix.de, akpm@...ux-foundation.org,
        torvalds@...ux-foundation.org, Claudiu.Beznea@...rochip.com
Subject: Re: About clk maintainership [Was: Re: [PULL] Add variants of
 devm_clk_get for prepared and enabled clocks enabled clocks]

Hi Russell, hi Stephen,

On Sat, Jul 31, 2021 at 12:41:19AM -0700, Stephen Boyd wrote:
> Quoting Russell King (Oracle) (2021-07-28 13:40:34)
> > > I adapted the Subject in the hope to catch Stephen's and Michael's
> > > attention. My impression is that this thread isn't on their radar yet,
> > > but the topic here seems important enough to get a matching Subject.
> 
> The thread is on my radar but...
> 
> > 
> > Have you thought about sending your pull request to the clk API
> > maintainer (iow, me) ?

I wasn't really aware that Russell has the clk API hat (or that this
separate hat actually exists and this isn't purely a CCF topic). I
assume I only did

	$ scripts/get_maintainer.pl -f drivers/clk/clk-devres.c

which is where the current and new code implementing devm_clk_get et al
lives.

@Russell: What is your position here, do you like the approach of
devm_clk_get_enabled? I can send a new pull request in your direction if
you like it and are willing to take it.

> +1 This patch doesn't fall under CCF maintainer.

Given that CCF is the only implementer of devm_clk_get at least an Ack
from your side would still be good I guess?

> Finally, this sort of patch has been discussed for years and I didn't
> see any mention of those previous attempts in the patch series. Has
> something changed since that time? I think we've got a bunch of hand
> rolled devm things in the meantime but not much else. 

I found a patch set adding devm variants of clk_enable (e.g.
https://lore.kernel.org/patchwork/patch/755667/) but this approach is
different as it also contains clk_get which IMHO makes more sense 
The discussion considered wrapping get+enable at one point, but I didn't
find a followup.

> I still wonder if it would be better if we had some sort of DT binding
> that said "turn this clk on when the driver probes this device and keep
> it on until the driver is unbound".

This doesn't sound like a hardware property and so I don't think this
belongs into DT and I would be surprised if the dt maintainers would be
willing to accept an idea with this semantic.

> That would probably work well for quite a few drivers that don't want
> to ever call clk_get() or clk_prepare_enable() and could tie into the
> assigned-clock-rates property in a way that let us keep the platform
> details out of the drivers. We could also go one step further and make
> a clk pm domain when this new property is present and then have the
> clk be enabled based on runtime PM of the device (and if runtime PM is
> disabled then just enable it at driver probe time).

clk pm domain sounds good, but introducing devm_clk_get_enabled() is
much easier and converting to it can be done without dt changes and more
or less mechanically. So I consider the cost-usage-value of
devm_clk_get_enabled() much better.

Best regards
Uwe

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

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