linux-kernel - Re: [PATCH RFC 0/2] clk: add metag specific gate/mux clocks

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Date:	Thu, 16 May 2013 10:56:51 +0100
From:	James Hogan <james.hogan@...tec.com>
To:	Stephen Boyd <sboyd@...eaurora.org>
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 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?)

> 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.

Cheers
James

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