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

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Message-ID: <20150914095846.0d8e2d74@bbrezillon>
Date:	Mon, 14 Sep 2015 09:58:46 +0200
From:	Boris Brezillon <boris.brezillon@...e-electrons.com>
To:	Harini Katakam <harinikatakamlinux@...il.com>
Cc:	Sören Brinkmann <soren.brinkmann@...inx.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

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.

Best Regards,

Boris

[1]http://lxr.free-electrons.com/source/Documentation/devicetree/bindings/clock/fixed-clock.txt

-- 
Boris Brezillon, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com
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