linux-kernel - Re: [PATCH 00/14] cpufreq: cpu0: Extend support beyond CPU0, V2

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Date:	Thu, 3 Jul 2014 08:14:04 +0530
From:	Viresh Kumar <viresh.kumar@...aro.org>
To:	Stephen Boyd <sboyd@...eaurora.org>,
	Mike Turquette <mturquette@...aro.org>
Cc:	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Lists linaro-kernel <linaro-kernel@...ts.linaro.org>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	Arvind Chauhan <arvind.chauhan@....com>,
	linux-arm-msm@...r.kernel.org, Sachin Kamat <spk.linux@...il.com>,
	Thomas P Abraham <thomas.ab@...sung.com>,
	Shawn Guo <shawn.guo@...aro.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Nishanth Menon <nm@...com>, Tomasz Figa <t.figa@...sung.com>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	Kukjin Kim <kgene.kim@...sung.com>,
	Michal Simek <michal.simek@...inx.com>,
	Rob Herring <rob.herring@...aro.org>,
	Santosh Shilimkar <santosh.shilimkar@...com>,
	Simon Horman <horms@...ge.net.au>
Subject: Re: [PATCH 00/14] cpufreq: cpu0: Extend support beyond CPU0, V2

On 3 July 2014 06:54, Stephen Boyd <sboyd@...eaurora.org> wrote:
> I gave it a spin. It works so you can have my
>
> Tested-by: Stephen Boyd <sboyd@...eaurora.org>

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..

@Mike: Is this less ugly ? :)
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