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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Date:   Tue, 3 Aug 2021 12:40:12 +0200
From:   Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
To:     Stephen Boyd <sboyd@...nel.org>
Cc:     Russell King <linux@...linux.org.uk>,
        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]

On Tue, Aug 03, 2021 at 01:11:54AM -0700, Stephen Boyd wrote:
> Quoting Russell King (Oracle) (2021-08-02 09:38:24)
> > On Mon, Aug 02, 2021 at 05:27:55PM +0200, Uwe Kleine-Konig wrote:
> > > Hello Russell,
> > > 
> > > On Mon, Aug 02, 2021 at 10:48:10AM +0100, Russell King (Oracle) wrote:
> > 
> > > > There have been several different approaches to wrapping things up,
> > > > but here's a question: should we make it easier to do the lazy thing
> > > > (get+enable) or should we make it easier to be power efficient?
> > > > Shouldn't we be encouraging people to write power efficient drivers?
> > > 
> > > Yeah, sounds compelling, but I wonder if that's of practical importance.
> > > How many driver authors do you expect to lure into making a better
> > > driver just because devm_clk_get_prepared() doesn't exist? In contrast:
> > > How many drivers become simpler with devm_clk_get_prepared() and so
> > > it becomes easier to maintain them and easier to spot bugs?
> > > In the absence of devm_clk_get_prepared(), is it better that several
> > > frameworks (or drivers) open code it?
> > 
> > It probably depends on where you stand on power management and power
> > efficiency issues. Personally, I would like to see more effort put
> > into drivers to make them more power efficient, and I believe in the
> > coming years, power efficiency is going to become a big issue.
> > 
> 
> I agree we should put more effort into power efficiency in the kernel.
> I've occasionally heard from driver writers that they never will turn
> the clk off even in low power modes though. They feel like it's a
> nuisance to have to do anything with the clk framework in their driver.
> When I say "why not use runtime PM?" I get told that they're not turning
> the clk off because it needs to be on all the time, so using runtime PM
> makes the driver more complicated, not less, and adds no value. I think
> some touchscreens are this way, and watchdogs too. Looking at the
> drivers being converted in this series I suspect RTC is one of those
> sorts of devices as well. But SPI and I2C most likely could benefit from
> using runtime PM and so those ones don't feel appropriate to convert.
> 
> Maybe this series would be more compelling if those various drivers that
> are hand rolling the devm action were converted to the consolidated
> official devm function. The truth is it's already happening in various
> subsystems so consolidating that logic into one place would be a win
> code size wise and very hard to ignore.
> 
> Doing
> 
>  $ git grep devm_add_action | grep clk
> 
> seems to catch quite a few of them.

Another upside is that grepping for these drivers with a potential for
further improvement become easier to grep for as
devm_clk_get_{prepared,enabled} is a much better hint :-)

The changes to these drivers probably won't go through a clk tree, so
adding these patches before adding devm_clk_get_enabled() would only
help for the warm and cozy feeling that it is right to do so, correct?

As my focus is limited to (mostly) drivers/pwm and I already have quite
some other patch quests on my list:

So can I lure you in merging the new functions and I will create a
kernel janitor task to convert more existing drivers?

Best regards
Uwe

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

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