[PATCH v3 3/5] clk: introduce the common clock framework

[Turquette, Mike]

On Thu, Dec 1, 2011 at 6:42 AM, Mark Brown
<broonie at opensource.wolfsonmicro.com> wrote:
> On Wed, Nov 30, 2011 at 11:39:59PM -0700, Paul Walmsley wrote:
>
>> Clock rate/parent-change notifiers are requirements for DVFS use-cases,
>> and they must be paired with something like the
>> clk_{allow,block}_rate_change() functions to work efficiently.  I intend
>> to comment on this later; it's not a simple problem.  It might be worth
>> noting that Tero and I implemented a simplified version of this for the
>> N900.
>
> I'm thinking that if we're going to have clk_{allow,block}_rate_change()
> we may as well make that the main interface to enable rate changes - if
> a device wants to change the clock rate it allows rate changes using
> that interface rather than by disabling the clocks.  I've got devices
> which can do glitch free updates of active clocks so having to disable
> would be a real restriction, and cpufreq would have issues with actually
> disabling the clock too I expect.
>

I agree that imposing a "disable clk before changing rate" policy in
the framework core is a bad idea.  During discussion on the
CLK_GATE_SET_RATE flag in the patch #2 Shawn commented that he has
some clks that must be enabled to change their rates (I assume he
means PLLs but that detail doesn't really matter).

Regards,
Mike