Quoting Viresh Kumar (2014-07-02 19:44:04)
> On 3 July 2014 06:54, Stephen Boyd <sboyd@xxxxxxxxxxxxxx> wrote:
> > I gave it a spin. It works so you can have my
> >
> > Tested-by: Stephen Boyd <sboyd@xxxxxxxxxxxxxx>
>
> Thanks, all suggested improvements are made and pushed again with
> your Tested-by..
>
> > I'm still concerned about the patch where we figure out if the clocks
> > are shared. I worry about a configuration where there are different
> > clocks for on/off (i.e. gates) that are per-cpu but they all source from
> > the same divider or something that is per-cluster. In DT this may be
> > described as different clock provider outputs for the gates and in the
> > cpu node we would have different clock specifiers but in reality all the
> > CPUs in that cluster are affected by the same frequency scaling.
>
> Yeah, this is probably what matches with Rob's doubt. These can
> actually be different. Good point.
>
> > In this case we'll need to get help from the clock framework to
> > determine that those gates clocks don't have any .set_rate() callback so
> > they can't actually change rate independently, and then walk up the tree
> > to their parents to see if they have a common ancestor that does change
> > rates. That's where it becomes useful to have a clock framework API for
> > this, like clk_shares_rate(struct clk *clk, struct clk *peer) or
> > something that can hide all this from cpufreq. Here's what I think it
> > would look like (totally untested/uncompiled):
> >
> > static struct clk *find_rate_changer(struct clk *clk)
> > {
> >
> > if (!clk)
> > return NULL;
> >
> > do {
> > /* Rate could change by changing parents */
> > if (clk->num_parents > 1)
> > return clk;
> >
> > /* Rate could change by calling clk_set_rate() */
> > if (clk->ops->set_rate)
> > return clk;
> >
> > /*
> > * This is odd, clk_set_rate() doesn't propagate
> > * and this clock can't change rate or parents
> > * so we must be at the root and the clock we
> > * started at can't change rates. Just return the
> > * root so that we can see if the other clock shares
> > * the same root although CPUfreq should never care.
> > */
> > if (!(clk->flags & CLK_SET_RATE_PARENT))
> > return clk;
> > } while ((clk = clk->parent))
> >
> > return NULL;
> > }
> >
> > bool clk_shares_rate(struct clk *clk, struct clk *peer)
> > {
> > struct clk *p1, *p2;
> >
> > p1 = find_rate_changer(clk);
> > p2 = find_rate_changer(peer)
> >
> > return p1 == p2;
> > }
>
> I find it much better then doing what I did initially, simply matching clk_get()
> outputs. Lets see what Mike has to say..
Sorry for being dense, but I still do not get why trying to dynamically
discover a shared rate-changeable clock is a better approach than simply
describing the hardware in DT?
Is adding a property to the CPU binding that describes how the CPUs in a
cluster expect to use a clock somehow a non-starter? It is certainly a
win for readability when staring at DT and trying to understand how DVFS
on that CPU is meant to work (as opposed to hiding that knowledge behind
a tree walk).
Regards,
Mike
>
> @Mike: Is this less ugly ? :)
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