Re: [PATCH v2 1/2] ARM: topology: Use a clock if possible to get the CPU frequency

[Maxime Ripard <maxime.ripard-wi1+55ScJUtKEb57/3fJTNBPR1lH4CV8@public.gmane.org>]

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On Mon, Jun 30, 2014 at 12:39:26PM +0200, Vincent Guittot wrote:
> On 30 June 2014 12:29, Russell King - ARM Linux <linux-lFZ/pmaqli7XmaaqVzeoHQ@public.gmane.org> wrote:
> > On Mon, Jun 30, 2014 at 12:12:22PM +0200, Maxime Ripard wrote:
> >> The Cortex-A7 and Cortex-A15 based SoCs need a clock-frequency property in the
> >> topology code.
> >>
> >> Allow to use a clock to provide the same information.
> >>
> >> Signed-off-by: Maxime Ripard <maxime.ripard-wi1+55ScJUtKEb57/3fJTNBPR1lH4CV8@public.gmane.org>
> >
> > This looks fine to me, but I don't know this code.  Maybe Vincent Guittot
> > should be on the To: list (added)?
> 
> Thanks

Ah, sorry for that.

> 
> >
> >> ---
> >>  arch/arm/kernel/topology.c | 25 ++++++++++++++++++-------
> >>  1 file changed, 18 insertions(+), 7 deletions(-)
> >>
> >> diff --git a/arch/arm/kernel/topology.c b/arch/arm/kernel/topology.c
> >> index 9d853189028b..268443d88094 100644
> >> --- a/arch/arm/kernel/topology.c
> >> +++ b/arch/arm/kernel/topology.c
> >> @@ -11,6 +11,7 @@
> >>   * for more details.
> >>   */
> >>
> >> +#include <linux/clk.h>
> >>  #include <linux/cpu.h>
> >>  #include <linux/cpumask.h>
> >>  #include <linux/export.h>
> >> @@ -100,8 +101,8 @@ static void __init parse_dt_topology(void)
> >>                                GFP_NOWAIT);
> >>
> >>       for_each_possible_cpu(cpu) {
> >> -             const u32 *rate;
> >> -             int len;
> >> +             struct clk *clk;
> >> +             u32 rate = 0;
> >>
> >>               /* too early to use cpu->of_node */
> >>               cn = of_get_cpu_node(cpu, NULL);
> >> @@ -117,14 +118,24 @@ static void __init parse_dt_topology(void)
> >>               if (cpu_eff->compatible == NULL)
> >>                       continue;
> >>
> >> -             rate = of_get_property(cn, "clock-frequency", &len);
> >> -             if (!rate || len != 4) {
> >> -                     pr_err("%s missing clock-frequency property\n",
> >> -                             cn->full_name);
> >> +             clk = of_clk_get(cn, 0);
> >> +             if (!IS_ERR(clk))
> >> +                     rate = clk_get_rate(clk);
> 
> We need the max frequency as it will be used to weight the different
> CPUs capacity. How do you ensure that the current clock rate is the
> max one ?

Hmm, the clock-frequency attribute in the ePAPR is defined at the
current CPU frequency, not the max one.

Maxime

-- 
Maxime Ripard, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com

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