linux-kernel - Re: [alsa-devel] [PATCH v2] clkdev: add devm_of_clk

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Date:   Tue, 29 Nov 2016 13:05:56 -0800
From:   Stephen Boyd <sboyd@...eaurora.org>
To:     Kuninori Morimoto <kuninori.morimoto.gx@...esas.com>
Cc:     Rob Herring <robh@...nel.org>,
        Linux-ALSA <alsa-devel@...a-project.org>,
        Linux-DT <devicetree@...r.kernel.org>,
        Michael Turquette <mturquette@...libre.com>,
        Russell King <linux@...linux.org.uk>,
        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: [alsa-devel] [PATCH v2] clkdev: add devm_of_clk_get()

On 11/24, Kuninori Morimoto wrote:
> 
> Hi Stephen, again
> 
> > > I've seen bindings that have the 'clocks' property at the top
> > > level and the appropriate 'clock-names' property to relate the
> > > clocks to a subnode.
> > > 
> > >  	sound_soc {
> > > 		clocks = <&xxx>, <&xxx>;
> > > 		clock-names = "cpu", "codec";
> > >  		...
> > >  		cpu {
> > >  			...
> > >  		};
> > >  		codec {
> > >  			...
> > >  		};
> > >  	};
> > > 
> > > Then the subnodes call clk_get() with the top level device and
> > > the name of their node and things match up. I suppose this
> > > binding is finalized though, so we can't really do that?
> > > 
> > > I see that the gpio framework has a similar design called
> > > devm_get_gpiod_from_child(), so how about we add a
> > > devm_get_clk_from_child() API? That would more closely match the
> > > intent here, which is to restrict the clk_get() operation to
> > > child nodes of the device passed as the first argument.
> > > 
> > > struct clk *devm_get_clk_from_child(struct device *dev,
> > > 				    const char *con_id,
> > > 				    struct device_node *child);
> 
> Thanks, but, my point is that Linux already have "of_clk_get()",
> but we don't have its devm_ version.
> The point is that of_clk_get() can get clock from "device_node".
> Why having devm_ version become so problem ?

The problem is that it encourages the use of of_clk_get() when
clk_get() is more desirable. Ideally of_clk_get() is never used
when a device exists. In this case, it seems like we need to
support it though, hence the suggestion of having a
devm_get_clk_from_child() API, that explicitly reads as "get a
clock from a child node of this device". The distinction is
important, because of_clk_get() should rarely be used.

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