linux-kernel - Re: [RFC PATCH 3/3] devicetree: macb: Add optional property tsu-clk

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Date:	Mon, 14 Sep 2015 07:44:23 -0700
From:	Sören Brinkmann <soren.brinkmann@...inx.com>
To:	Boris Brezillon <boris.brezillon@...e-electrons.com>
CC:	Harini Katakam <harinikatakamlinux@...il.com>,
	Harini Katakam <harini.katakam@...inx.com>,
	Nicolas Ferre <nicolas.ferre@...el.com>, <davem@...emloft.net>,
	Rob Herring <robh+dt@...nel.org>,
	Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	"ijc+devicetree@...lion.org.uk" <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>,
	<alexandre.belloni@...e-electrons.com>, <netdev@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	Punnaiah Choudary Kalluri <punnaia@...inx.com>,
	"michals@...inx.com" <michals@...inx.com>, <anirudh@...inx.com>
Subject: Re: [RFC PATCH 3/3] devicetree: macb: Add optional property tsu-clk

On Mon, 2015-09-14 at 09:58AM +0200, Boris Brezillon wrote:
> Hi Harini,
> 
> On Mon, 14 Sep 2015 09:39:05 +0530
> Harini Katakam <harinikatakamlinux@...il.com> wrote:
> 
> > On Fri, Sep 11, 2015 at 10:22 PM, Sören Brinkmann
> > <soren.brinkmann@...inx.com> wrote:
> > > Hi Harini,
> > >
> > > On Fri, 2015-09-11 at 01:27PM +0530, Harini Katakam wrote:
> > >> Add TSU clock frequency to be used for 1588 support in macb driver.
> > >>
> > >> Signed-off-by: Harini Katakam <harinik@...inx.com>
> > >> ---
> > >>  Documentation/devicetree/bindings/net/macb.txt |    3 +++
> > >>  1 file changed, 3 insertions(+)
> > >>
> > >> diff --git a/Documentation/devicetree/bindings/net/macb.txt b/Documentation/devicetree/bindings/net/macb.txt
> > >> index b5d7976..f7c0ea8 100644
> > >> --- a/Documentation/devicetree/bindings/net/macb.txt
> > >> +++ b/Documentation/devicetree/bindings/net/macb.txt
> > >> @@ -19,6 +19,9 @@ Required properties:
> > >>       Optional elements: 'tx_clk'
> > >>  - clocks: Phandles to input clocks.
> > >>
> > >> +Optional properties:
> > >> +- tsu-clk: Time stamp unit clock frequency used.
> > >
> > > Why are we not using the CCF and a clk_get_rate() in the driver?
> > >
> > 
> > If the clock source was only internal, we could use this
> > approach as usual. But TSU clock can be configured to
> > come from an external clock source or internal.
> 
> How about declaring a fixed-rate clk [1] if it comes from an external
> clk, and using a clk driver for the internal clk case?
> This way you'll be able to use the clk API (including the
> clk_get_rate() function) instead of introducing a new way to retrieve a
> clk frequency.

Right. Also, Zynq does already support external clock inputs (actually,
every clock originates from some external clock/oscillator at some
point). Maybe that code needs some additions to handle the TSU clock
too. But either way, I can't see why a clock cannot be modeled using the
CCF.

	Sören
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