linux-kernel - Re: [RFC 2/2] clk: samsung: Fix clock disable failure because domain being gated

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Message-id: <1416917945.29431.6.camel@AMDC1943>
Date:	Tue, 25 Nov 2014 13:19:05 +0100
From:	Krzysztof Kozlowski <k.kozlowski@...sung.com>
To:	Tomasz Figa <tomasz.figa@...il.com>
Cc:	Mike Turquette <mturquette@...aro.org>,
	Sylwester Nawrocki <s.nawrocki@...sung.com>,
	Kukjin Kim <kgene@...nel.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	"linux-samsung-soc@...r.kernel.org" 
	<linux-samsung-soc@...r.kernel.org>,
	linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
	Javier Martinez Canillas <javier.martinez@...labora.co.uk>,
	Vivek Gautam <gautam.vivek@...sung.com>,
	Kevin Hilman <khilman@...nel.org>
Subject: Re: [RFC 2/2] clk: samsung: Fix clock disable failure because domain
 being gated

On wto, 2014-11-25 at 20:35 +0900, Tomasz Figa wrote:
> Hi Krzysztof,
> 
> Please see my comments inline.
> 
> 2014-11-25 0:18 GMT+09:00 Krzysztof Kozlowski <k.kozlowski@...sung.com>:
> > +static int audss_clk_gate_enable(struct clk_hw *hw)
> > +{
> > +       int ret;
> > +
> > +       if (!IS_ERR(pll_in))
> > +               clk_prepare_enable(pll_in);
> 
> Calling clk_prepare_enable() from enable() callback doesn't look like
> a good idea, because enabling is not supposed to sleep, while
> preparing might do so.

Right.

> I guess you have to pre-prepare this clock in probe and then only call
> enable here.

Yes, the prepare won't have any negative effect on energy usage anyway.

> 
> > +       ret = clk_gate_ops.enable(hw);
> > +       if (!IS_ERR(pll_in))
> > +               clk_disable_unprepare(pll_in);
> > +
> > +       return ret;
> > +}
> 
> [snip]
> 
> > +/* TODO: Also mux and div */
> > +const struct clk_ops audss_clk_gate_ops = {
> 
> nit: static const probably?

Yes.

> 
> > +       .enable = audss_clk_gate_enable,
> > +       .disable = audss_clk_gate_disable,
> > +       .is_enabled = audss_clk_gate_is_enabled,
> > +};
> 
> As for the approach itself, maybe you should simply register fully
> custom clocks with clk_register(), without altering
> clk_register_gate() at all and simply calling gate ops whenever
> necessary? I don't know, just a loose idea.

Initially that seemed to me the simplest way to encapsulate gate_ops
calls. However in that approach I should also change clk_register_mux
and clk_register_divider... which complicates this patch and maybe your
idea will be simpler overall.

> By the way, this issue could be probably solved by integrating generic
> clocks with regmap API, since regmap-mmio can automatically control a
> clock.

Indeed but this looks like much bigger task.

Anyway thanks for feedback. I'll prepare another version.

Best regards,
Krzysztof


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