linux-kernel - Re: [PATCH v2] clk: add more managed APIs

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Message-ID: <20170131193437.GA7903@roeck-us.net>
Date:   Tue, 31 Jan 2017 11:34:37 -0800
From:   Guenter Roeck <linux@...ck-us.net>
To:     Dmitry Torokhov <dmitry.torokhov@...il.com>
Cc:     Stephen Boyd <sboyd@...eaurora.org>,
        Russell King - ARM Linux <linux@...linux.org.uk>,
        Michael Turquette <mturquette@...libre.com>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Andy Shevchenko <andy.shevchenko@...il.com>,
        linux-clk@...r.kernel.org, lkml <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] clk: add more managed APIs

On Tue, Jan 31, 2017 at 10:26:29AM -0800, Dmitry Torokhov wrote:
> On Tue, Jan 31, 2017 at 9:20 AM, Guenter Roeck <linux@...ck-us.net> wrote:
> > On Mon, Jan 30, 2017 at 04:59:57PM -0800, Dmitry Torokhov wrote:
> >> On Mon, Jan 30, 2017 at 11:22:14AM -0800, Guenter Roeck wrote:
> >> > On Mon, Jan 30, 2017 at 10:55:51AM -0800, Stephen Boyd wrote:
> >> > > On 01/29, Dmitry Torokhov wrote:
> >> > > > When converting a driver to managed resources it is desirable to be able to
> >> > > > manage all resources in the same fashion. This change allows managing
> >> > > > clocks in the same way we manage many other resources.
> >> > >
> >> > > Can you please add 'managing clock prepared and enabled state in
> >> > > the same way'?
> >> > >
> >> > > The current wording makes it sound like we don't have
> >> > > devm_clk_get() when we do.
> >> > >
> >> > > >
> >> > > > This adds the following managed APIs:
> >> > > >
> >> > > > - devm_clk_prepare()/devm_clk_unprepare();
> >> > > > - devm_clk_prepare_enable()/devm_clk_disable_unprepare().
> >> > >
> >> > > Wouldn't this be preceded by a devm_clk_get() call? Wouldn't it
> >> > > be even shorter to have the APIs
> >> > >
> >> > >   devm_clk_get_and_prepare()/devm_clk_unprepare_and_put()
> >> > >   devm_clk_get_and_prepare_enable()/devm_clk_disable_unprepare_and_put()
> >> > >
> >> > > instead?
> >> > >
> >> > In many cases I see
> >> >
> >> >     devm_clk_get(clk1);
> >> >     devm_clk_get(clk2);
> >> >     clk_prepare_enable(clk1);
> >> >     clk_prepare_enable(clk2);
> >> >
> >> > Sometimes the calls are intertwined with setting the clock rates.
> >> >
> >> >     devm_clk_get(clk);
> >> >     clk_set_rate(clk, rate);
> >> >     clk_prepare_enable(clk);
> >> >
> >> > Maybe the additional calls make sense; I can imagine they would.
> >> > However, I personally would be a bit wary of changing the initialization
> >> > order of multi-clock initializations, and I am not sure how a single call
> >> > could address setting the rate ([devm_]clk_get_setrate_prepare_enable()
> >> > seems like a bit too much).
> >> >
> >> > [ On a side note, why is there no clk_get_prepare_enable() and
> >> >   clk_get_prepare() ? Maybe it would be better to introduce those
> >> >   together with the matching devm_ functions in a separate patch
> >> >   if they are useful. ]
> >> >
> >> > > Is there any other subsystem that has similar functionality?
> >> > > Regulators? GPIOs? Resets? I'm just curious if those subsystems
> >> > > also need similar changes.
> >> > >
> >> > Ultimately yes, and most already do. If I recall correctly, I tried to
> >> > introduce devm_ functions for regulators some time ago, but that was
> >> > rejected with the comment that it would invite misuse.  At the time
> >> > I accepted that; today my reaction would be to counter that pretty much
> >> > everything can be misused, and that the potential for misuse should not
> >> > penaltize all the valid use cases.
> >>
> >> I think we should ping Mark again. The only thing we are achieving is
> >> that everyone is using devm_add_action_or_reset() with wrappers around
> >> regulator_put().
> >>
> > regulator_get() has an equivalent devm_regulator_get(). Maybe it was since
> > added, or I was thinking about a different function.
> 
> I think we also need devm_regulator_enable().
> 
Ah, yes, that was it [1]. And, yes, I do see some devm_add_action() calls
around regulator_enable().

Guenter

---
[1] https://lkml.org/lkml/2014/2/1/131