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

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Date:   Mon, 30 Jan 2017 11:22:14 -0800
From:   Guenter Roeck <linux@...ck-us.net>
To:     Stephen Boyd <sboyd@...eaurora.org>
Cc:     Dmitry Torokhov <dmitry.torokhov@...il.com>,
        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 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.

Thanks,
Guenter