linux-kernel - Re: [PATCH 15/15] metag: tz1090: add TZ1090 clocks to device tree

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Date:	Tue, 25 Nov 2014 11:39:23 +0000
From:	James Hogan <james.hogan@...tec.com>
To:	Heiko Stübner <heiko@...ech.de>
CC:	Mike Turquette <mturquette@...aro.org>,
	<linux-metag@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<devicetree@...r.kernel.org>, Rob Herring <robh+dt@...nel.org>,
	Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	"Kumar Gala" <galak@...eaurora.org>
Subject: Re: [PATCH 15/15] metag: tz1090: add TZ1090 clocks to device tree

On 24/11/14 23:03, Heiko Stübner wrote:
> Am Freitag, 21. November 2014, 10:06:47 schrieb James Hogan:
>> On Thu, Nov 20, 2014 at 01:56:24PM +0100, Heiko Stübner wrote:
>>> I don't know enough about your clock structure, but it looks quite a bit
>>> like Mike's mail from May [0] may apply here too.
>>>
>>> The register layout also suggests that it is indeed one clock ip-block:
>>>
>>> 0x02005908 0x4	CR_TOP_CLKSWITCH
>>> 0x0200590c 0x4	CR_TOP_CLKENAB
>>> 0x02005950 0x4	CR_TOP_SYSPLL_CTL0
>>> 0x02005954 0x4	CR_TOP_SYSPLL_CTL1
>>> 0x02005988 0x4	CR_TOP_CLKSWITCH2
>>> 0x0200598c 0x4	CR_TOP_CLKENAB2
>>> ...
>>>
>>>
>>> [0] https://lkml.org/lkml/2014/5/14/715
>>
>> Thanks, that does make sense. It's probably more like 4 memory regions
>> ("top" level, "perip" peripheral registers, "hep" high end peripheral
>> registers, and "pdc" powerdown controller registers), but it could
>> certainly still have a single binding with multiple memory regions to
>> simplify the clock specifiers.
> 
> It could also make sense to have 4 clock controller nodes for those. I guess 
> it all depends on how the hardware is layed out.
> 
> For example on Rockchip SoCs, all of this is contained in the "APB CRU" (Clock 
> and Reset Unit) with a memory region of <0x20000000 0x4000> - so here one 

/me twigs what CRU stands for!

> hardware-block that contains all the clocks and also the reset controller.
> 
> On the other hand it might very well be more than one ip-block on your 
> platform. 
> 
> So I guess it comes down to looking at the memory map [or documentation :-) ] 
> to determine how many ip blocks there really are.

I'll probably combine the TOP and HEP ones at least. HEP clock stuff is
much simpler than TOP, and a couple of clocks feed both ways between
them which otherwise wouldn't need to be visible, suggesting they're
pretty closely coupled.

PERIP is pretty much a single bank of 14 system clock gates for
individual peripherals, so that one's arguable. I'll probably separate
it as there's only 1 input clock so it wouldn't be at all messy.

PDC is pretty independent and can remain mostly unchanged (that is
consistent with irq, pinctrl and gpio drivers too, where PDC low power
stuff is independent and fits nicely into separate drivers).

Thanks for the suggestions!

James


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