linux-kernel - Re: [PATCH] clk: zynq: avoid retrieving clock names from DT property

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Date:	Mon, 18 Jul 2016 10:22:44 -0700
From:	Sören Brinkmann <soren.brinkmann@...inx.com>
To:	Masahiro Yamada <yamada.masahiro@...ionext.com>
CC:	<linux-clk@...r.kernel.org>,
	Michal Simek <michal.simek@...inx.com>,
	<devicetree@...r.kernel.org>,
	Michael Turquette <mturquette@...libre.com>,
	Stephen Boyd <sboyd@...eaurora.org>,
	<linux-kernel@...r.kernel.org>, "Rob Herring" <robh+dt@...nel.org>,
	Mark Rutland <mark.rutland@....com>,
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH] clk: zynq: avoid retrieving clock names from DT property

On Sun, 2016-07-17 at 09:11:10 -0700, Sören Brinkmann wrote:
> On Sun, 2016-07-17 at 00:15:23 +0900, Masahiro Yamada wrote:
> > The "clock-output-names" property is useful for generic clock
> > providers such as fixed-clock, fixed-factor-clock, etc.
> > 
> > On the other hand, it should not be used for really SoC-specific
> > clock providers like this one.  As you see in "enum zynq_clk" in
> > this driver, it is written as if it already knows all the clock
> > names.  Besides, this is instantiated only once, so no clock name
> > conflict would happen even if the clock names are hard-coded in the
> > driver.
> > 
> > The device tree (arch/arm/boot/dts/zynq-7000.dtsi) will be fixed
> > later.
> > 
> > Signed-off-by: Masahiro Yamada <yamada.masahiro@...ionext.com>
> 
> IIRC, this was the only way to allow circular clock routing. E.g. there
> are use-cases that route an FCLK back into the PS to use it as input for
> the GEM. With the introduction of deferred probing this might all be
> possible now but it would be good to verify that this kind of circular
> clock routing still works with this change.

Yep, this breaks this kind of routing. E.g. if you remove the
clk-output-names from the DT and add an EMIO clock input like this:
	clocks = <&clkc 15>;
	clock-names = "gem1_emio_clk";
the code will no longer be able to correctly obtain the clock name for that input.

	Sören