linux-kernel - Re: [PATCH 2/3] ASoC: simple-card: use devm_get_clk_from

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Message-ID: <20161209002837.GE5423@codeaurora.org>
Date:   Thu, 8 Dec 2016 16:28:37 -0800
From:   Stephen Boyd <sboyd@...eaurora.org>
To:     Kuninori Morimoto <kuninori.morimoto.gx@...esas.com>
Cc:     Russell King - ARM Linux <linux@...linux.org.uk>,
        Rob Herring <robh@...nel.org>,
        Linux-ALSA <alsa-devel@...a-project.org>,
        Linux-DT <devicetree@...r.kernel.org>,
        Michael Turquette <mturquette@...libre.com>,
        Linux-Kernel <linux-kernel@...r.kernel.org>,
        Mark Brown <broonie@...nel.org>, linux-clk@...r.kernel.org,
        Linux-ARM <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH 2/3] ASoC: simple-card: use devm_get_clk_from_child()

On 12/09, Kuninori Morimoto wrote:
> 
> Hi Stephen
> 
> > > @@ -111,14 +112,13 @@ int asoc_simple_card_parse_clk(struct device_node *node,
> > >  	 *  or "system-clock-frequency = <xxx>"
> > >  	 *  or device's module clock.
> > >  	 */
> > > -	clk = of_clk_get(node, 0);
> > > +	clk = devm_get_clk_from_child(dev, node, NULL);
> > >  	if (!IS_ERR(clk)) {
> > >  		simple_dai->sysclk = clk_get_rate(clk);
> > > -		simple_dai->clk = clk;
> > >  	} else if (!of_property_read_u32(node, "system-clock-frequency", &val)) {
> > >  		simple_dai->sysclk = val;
> > >  	} else {
> > > -		clk = of_clk_get(dai_of_node, 0);
> > > +		clk = devm_get_clk_from_child(dev, dai_of_node, NULL);
> > 
> > 
> > I was confused for a minute about how the second of_clk_get()
> > call with the dai_link node could work. Is that documented
> > anywhere or used by anyone? It seems like it's at least another
> > child node of the sound node (which is dev here) so it seems ok.
> 
> Documentation/devicetree/bindings/sound/simple-card.txt
> explains 1st of_clk_get will be used as "if needed",
> 2nd of_clk_get will be used as "not needed pattern".
> 1st pattern will use specific clock, 2nd pattern will use
> "cpu" or "codec" clock.
> 2nd one was added by someone (I forgot), and many driver is
> based on this feature.
> 

Can you point to some dts file in the kernel that falls into the
devm_get_clk_from_child(dev, dai_of_node, NULL) part?

-- 
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