linux-kernel - Re: [PATCH] clk-rcar-gen2: RCAN clock support

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Date:	Wed, 10 Sep 2014 13:36:50 +0300
From:	Laurent Pinchart <laurent.pinchart@...asonboard.com>
To:	Sergei Shtylyov <sergei.shtylyov@...entembedded.com>
Cc:	Geert Uytterhoeven <geert@...ux-m68k.org>,
	Mike Turquette <mturquette@...aro.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Linux-sh list <linux-sh@...r.kernel.org>,
	Pavel Kiryukhin <vksavl@...il.com>
Subject: Re: [PATCH] clk-rcar-gen2: RCAN clock support

Hi Sergei,

On Friday 05 September 2014 17:33:28 Sergei Shtylyov wrote:
> On 09/05/2014 01:03 PM, Geert Uytterhoeven wrote:
> >>> Add RCAN clock support to the R-Car generation 2 CPG driver. This clock
> >>> gets derived from the USB_EXTAL clock by dividing it by 6. The layout of
> >>> RCANCKCR register is close to those of the clocks supported by the 'clk-
> >>> div6' driver but has no divider field, and so can't be supported by that
> >>> driver...
> >>> 
> >>> Signed-off-by: Sergei Shtylyov <sergei.shtylyov@...entembedded.com>
> >>> 
> >>> ---
> >>> The patch is against the 'clk-next' branch of Mike Turquette's
> >>> 'linux.git' repo.
> >>> 
> >>>  drivers/clk/shmobile/clk-rcar-gen2.c |   99 +++++++++++++++++++++++++++
> >>>  1 file changed, 99 insertions(+)
> >>>    
> >> More than a months has passed, there hasn't been any feedback, patch
> >> 
> >> hasn't been applied... what's wrong with it?
> > 
> > Sorry for missing this, it went under my radar.
> > 
> > I'm not a clock expert (pulling in Laurent), but it looks fine to me.
> > I'm just wondering whether you can simplify the code by using clk-gate?
> 
> The gated clocks inherit their clock rate from the parent, while the RCAN
> clock has a fixed divisor (6). I'm gonna look into composite clocks instead.

The composite clock looks like it would indeed simplify the code. If that's 
the case I would prefer that solution.

Please also remember to update the CPG DT bindings documentation to add the 
rcan clock and the USB input clock. On that subject, do you know what other 
clocks derive from the USB input clock ? The documentation isn't clear.

I'm also a bit puzzled by V2H that, according to the datasheet, lacks the 
RANCKCR register, but has a RCAN clock with a dedicated RCAN divider in the 
CPG diagram. I think Geert and Morimoto-san are investigating this.

-- 
Regards,

Laurent Pinchart

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