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

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Message-ID: <20170131005957.GB35974@dtor-ws>
Date:   Mon, 30 Jan 2017 16:59:57 -0800
From:   Dmitry Torokhov <dmitry.torokhov@...il.com>
To:     Guenter Roeck <linux@...ck-us.net>
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, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] clk: add more managed APIs

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().

As I said elsewhere, there are "always used" devices where it isn't
worth it to postpone enabling regulators.

Thanks.

-- 
Dmitry