[PATCH 1/2] ARM: imx6q: add pll round_rate support

[s.hauer@pengutronix.de (Sascha Hauer)]

On Fri, Mar 16, 2012 at 09:10:07AM +0800, Richard Zhao wrote:
> Hi Sascha,
> 
> On Thu, Mar 15, 2012 at 07:50:04PM +0100, Sascha Hauer wrote:
> > On Thu, Mar 15, 2012 at 11:15:23PM +0800, Richard Zhao wrote:
> > > On Thu, Mar 15, 2012 at 04:00:48PM +0100, Sascha Hauer wrote:
> > > > On Thu, Mar 15, 2012 at 10:46:04PM +0800, Richard Zhao wrote:
> > > > > On Wed, Mar 14, 2012 at 09:52:28AM +0100, Sascha Hauer wrote:
> > > > > > On Wed, Mar 14, 2012 at 04:22:58PM +0800, Richard Zhao wrote:
> > > > > > > Signed-off-by: Richard Zhao <richard.zhao@linaro.org>
> > > > > > > ---
> > > > > > >  
> > > > > > >  #define DEF_PLL(name)					\
> > > > > > >  	static struct clk name = {			\
> > > > > > > @@ -681,6 +741,7 @@ static int pll_set_rate(struct clk *clk, unsigned long rate)
> > > > > > >  		.disable	= pll_disable,		\
> > > > > > >  		.get_rate	= name##_get_rate,	\
> > > > > > >  		.set_rate	= name##_set_rate,	\
> > > > > > > +		.round_rate	= name##_round_rate,	\
> > > > > > 
> > > > > > I hope this ## stuff is gone soon with the generic clock framework. It
> > > > > > is so ugly and inefficient.
> > > > > I hope this doesn't prevent this two patches go in.
> > > > 
> > > > Given that we are short from getting a generic clock framework (and I
> > > > think this time it's for real) and that you are not mention in any words
> > > > what these patches fix I don't see a reason for merging them.
> > > I think the cpu clock is a great challenge for generic clock framework.
> > > When it set_rate, it includes reparent, and change parent's parent's rate.
> > > I don't see any upstream code like that till now. and it's really what
> > > we need.
> > 
> > Then do a clk_set_parent, clk_set_rate and a clk_set_parent again
> > in your cpufreq driver.
> No, it's platform code, and supposed to be in arch/arm. What the cpufre
> driver know is to get cpu clk, rather not how cpu clk change its rate.
> And cpu clk/arm_clk is a real clock wires in SoC.

The job of the clock framework is to give a consistent view on the
clocks and to handle parent/rate changes properly. It even the
CLK_SET_RATE_GATE for ensuring that your PLL can only change its rate
when it's gated. It's not the job of the clock framework to dynamically
reorganize the clock tree on a rate change.

Besides, do you really want to reprogram the PLL with a cpufreq change?
You have a divider behind that PLL which you apparently can change
without having to reparent the PLL. Doesn't this give you enough choices
for the cpu frequency?

> > The notifying mechanism even allows you to
> > block any concurrent change in between these three steps if necessary.
> > Noone says that these three steps have to be encapsulated in a single
> > clk_set_rate call like you did in your patch.
> If you're reviwing the patch, why not take a step advance? :)

I have prepared the patches for converting i.MX1/21/25/27 and I have
(older) patches for the i.MX31/51/53 which I want to rebase on the
current clock framework. That gives me enough to do until the next merge
window. Additionally I'm not yet very familiar with the i.MX6.

Sascha

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