Message-ID: <51955C2C.5060705@codeaurora.org>
Date:	Thu, 16 May 2013 15:22:36 -0700
From:	Stephen Boyd <sboyd@...eaurora.org>
To:	James Hogan <james.hogan@...tec.com>
CC:	Mike Turquette <mturquette@...aro.org>,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	Arnd Bergmann <arnd@...db.de>,
	"devicetree-discuss@...ts.ozlabs.org" 
	<devicetree-discuss@...ts.ozlabs.org>,
	Rob Herring <rob.herring@...xeda.com>,
	Grant Likely <grant.likely@...aro.org>
Subject: Re: [PATCH RFC 0/2] clk: add metag specific gate/mux clocks

On 05/16/13 02:56, James Hogan wrote:
> On 15/05/13 23:31, Stephen Boyd wrote:
>> On 05/10/13 08:02, James Hogan wrote:
>>> This adds a metag architecture specific clk-gate and clk-mux which
>>> extends the generic ones to use global lock2 to protect the register
>>> fields. It is common with metag to have an RTOS running on a different
>>> thread or core with access to different bits in the same register (which
>>> contain clock gate/switch bits for other clocks). Access to such
>>> registers must be serialised with a global lock such as the one provided
>>> by the metag architecture port in <asm/global_lock.h>
>>>
>>> RFC because despite extending the generic clocks there's still a bit of
>>> duplicated code necessary. One alternative is to add special cases to
>>> the generic clock components for when a global or callback function
>>> based lock is desired instead of a spinlock, but I wasn't sure if that
>>> sort of hack would really be appreciated in the generic drivers.
>>>
>>> Comments?
>> Can you please Cc the devicetree mailing list when proposing new bindings?
> Erm, I think it was on Cc (devicetree-discuss@...ts.ozlabs.org yeh?)

I added them in my reply.

>
>> Your patchset brings up a question I've had which is if we should be
>> putting the bits and register width information in devicetree at all. On
>> the one hand it's nice to not have anything in C code, just iterate over
>> nodes and register clocks. On the other hand, it's the first time I've
>> seen anyone put the register interface into devicetree. From what I can
>> tell, the regulator bindings have put at most the register base and
>> physical properties like enable-time, max voltage, etc., but not what
>> bits are needed to enable/disable a regulator. Also I thought I read
>> somewhere that reg properties shouldn't overlap each other, so if you
>> ever have two clocks living in the same register we're going to violate
>> that.
> Oh, I wasn't aware of that limitation.
>
> The SoC I'm working with has some registers full of clock enable bits (I
> guess one could have a gate array component with up to 32 clock inputs
> and outputs) and some registers full of clock mux switch bits (that
> would get really messy to define as a block since each bit switches
> between 2 parents, and some of the parents are other clock muxes in the
> same block). Some registers contain a bunch of low power related bits
> together, including clock enable bits in the same register as various
> pinconf settings which is used by a separate pinctrl driver.
>

I have similar hardware and so I would like to hear what the devicetree
knowledgeable people think about it. Hopefully Rob or Grant can shed
some light here.

-- 
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