* RE: Regarding CPU frequency reported by Salvator-X board
2019-10-14 7:54 ` Regarding CPU frequency reported by Salvator-X board Geert Uytterhoeven
@ 2019-12-13 11:57 ` Biju Das
0 siblings, 0 replies; 2+ messages in thread
From: Biju Das @ 2019-12-13 11:57 UTC (permalink / raw)
To: Geert Uytterhoeven
Cc: Geert Uytterhoeven, Simon Horman, linux-renesas-soc, Dien Pham,
TAKESHI KIHARA, Niklas Söderlund, Stephen Boyd,
Michael Turquette, linux-clk
Hi All,
Any update on this issue.
Regards,
Biju
> -----Original Message-----
> From: Geert Uytterhoeven <geert@linux-m68k.org>
> Sent: Monday, October 14, 2019 8:54 AM
> To: Biju Das <biju.das@bp.renesas.com>
> Cc: Geert Uytterhoeven <geert+renesas@glider.be>; Simon Horman
> <horms@verge.net.au>; linux-renesas-soc@vger.kernel.org; Dien Pham
> <dien.pham.ry@rvc.renesas.com>; TAKESHI KIHARA
> <takeshi.kihara.df@renesas.com>; Niklas Söderlund
> <niklas.soderlund+renesas@ragnatech.se>; Stephen Boyd
> <sboyd@kernel.org>; Michael Turquette <mturquette@baylibre.com>;
> linux-clk <linux-clk@vger.kernel.org>
> Subject: Re: Regarding CPU frequency reported by Salvator-X board
>
> Hi Biju,
>
> CC clk
>
> On Mon, Oct 14, 2019 at 9:46 AM Biju Das <biju.das@bp.renesas.com>
> wrote:
> > I have further investigated this issue, please find my findings below
> >
> > The "cpg_z_clk_round_rate" function is called 2 times from
> "dev_pm_opp_set_rate" (1 is direct call and other through "clk_set_rate")
> function.
> >
> > For 500000000 frequency, after doing math operation(mult =
> > div_u64(rate * 32ULL, prate);), it gets a factor 10--> 10.66
> > truncated to 10 and the frequency returned by the system is 468748125
> >
> > On the second " cpg_z_clk_round_rate ", the below function make the
> value to worse, it gets a value of 9.9999, since it is integer division it is
> truncated to 9.
> > mult = div_u64(rate * 32ULL, prate);
> >
> > Now the frequency 468748125, after doing math operation becomes
> 421874 KHz. This is the problem.
> >
> > So I think the div_64 is wrong here, Instead we could go with
> DIV64_U64_ROUND_CLOSEST.
> >
> > With "DIV64_U64_ROUND_CLOSEST" the factor is 10.66 which is rounded
> to 11.
> >
> > So for 500000, after math operation, it becomes 515624
> >
> > Please share your opinion this issue.
>
> I don't know what's the best way to solve this.
>
> Rounding instead of truncating may lead to programming a too high clock
> frequency, which might damage the hardware.
>
> Please note that the current code no longer uses div_u64(), but div64_ul()
> instead, which should have no impact on your findings.
>
> > > -----Original Message-----
> > > From: Biju Das
> > > Sent: Thursday, September 19, 2019 11:49 AM
> > > To: Geert Uytterhoeven <geert+renesas@glider.be>; Simon Horman
> > > <horms@verge.net.au>; linux-renesas-soc@vger.kernel.org; Dien Pham
> > > <dien.pham.ry@rvc.renesas.com>; TAKESHI KIHARA
> > > <takeshi.kihara.df@renesas.com>; Niklas Söderlund
> > > <niklas.soderlund+renesas@ragnatech.se>
> > > Subject: Regarding CPU frequency reported by Salvator-X board
> > >
> > > Hi All,
> > >
> > > I started testing frequency mentioned in OPP table with M3-W1.1
> > > Salvator-X board (NOT salvator-XS) using user space governor
> > >
> > > The actual frequency reported for 0.5GHz(500000 KHz) is too much
> > > deviated from the target frequency [INFO] Target frequency: 500000
> > > KHz [INFO] Actual frequency: 421874 KHz
> > >
> > > But if I change the extal value, as per the board schematic
> > > (16.6666MHz), the value is some what closer to target frequency.
> > > &extal_clk {
> > > - clock-frequency = <16666666>;
> > > + clock-frequency = <16666600>;
> > > };
> > > [INFO] Target frequency: 500000 KHz
> > > [INFO] Actual frequency: 468748 KHz
> > >
> > > Q1) Have any one seen this issue? Please share your thoughts on this
> issue.
> > >
> > > Note:-
> > > I am not seeing this issue on Salvator-XS board, where the extal_clk
> > > value= 16640000(16.64MHz).
> > >
> > > Please see the logs
> > > with clock-frequency = <16666666>;
> > > -----------------------------------------------
> > > root@salvator-x:/cip-test-scripts# ./opp_t_001.sh [INFO] Testing
> > > cpufreq for
> > > policy:
> > > [INFO] /sys/devices/system/cpu/cpufreq/policy0
> > > [INFO]
> > > [INFO] CPUs affected:
> > > [INFO] 0 1
> > > [INFO]
> > > [INFO] Available frequencies:
> > > [INFO] 500000 1000000 1500000
> > > [INFO]
> > > [INFO] Target frequency: 500000 KHz [INFO] Actual frequency:
> > > 421874 KHz [INFO] [INFO] Target frequency: 1000000 KHz [INFO]
> > > Actual frequency: 937499 KHz [INFO] [INFO] Target frequency:
> > > 1500000 KHz [INFO] Actual frequency: 1499999 KHz [INFO] [INFO]
> > > Testing cpufreq for policy:
> > > [INFO] /sys/devices/system/cpu/cpufreq/policy2
> > > [INFO]
> > > [INFO] CPUs affected:
> > > [INFO] 2 3 4 5
> > > [INFO]
> > > [INFO] Available frequencies:
> > > [INFO] 800000 1000000 1200000
> > > [INFO]
> > > [INFO] Target frequency: 800000 KHz [INFO] Actual frequency:
> > > 749999 KHz [INFO] [INFO] Target frequency: 1000000 KHz [INFO]
> > > Actual frequency: 974999 KHz [INFO] [INFO] Target frequency:
> > > 1200000 KHz [INFO] Actual frequency: 1199999 KHz
> > >
> > > With clock-frequency = <16666600>
> > > ----------------------------------------------
> > > root@salvator-x:/cip-test-scripts# ./opp_t_001.sh [INFO] Testing
> > > cpufreq for
> > > policy:
> > > [INFO] /sys/devices/system/cpu/cpufreq/policy0
> > > [INFO]
> > > [INFO] CPUs affected:
> > > [INFO] 0 1
> > > [INFO]
> > > [INFO] Available frequencies:
> > > [INFO] 500000 1000000 1500000
> > > [INFO]
> > > [INFO] Target frequency: 500000 KHz [INFO] Actual frequency:
> > > 468748 KHz [INFO] [INFO] Target frequency: 1000000 KHz [INFO]
> > > Actual frequency: 937496 KHz [INFO] [INFO] Target frequency:
> > > 1500000 KHz [INFO] Actual frequency: 1499994 KHz [INFO] [INFO]
> > > Testing cpufreq for policy:
> > > [INFO] /sys/devices/system/cpu/cpufreq/policy2
> > > [INFO]
> > > [INFO] CPUs affected:
> > > [INFO] 2 3 4 5
> > > [INFO]
> > > [INFO] Available frequencies:
> > > [INFO] 800000 1000000 1200000
> > > [INFO]
> > > [INFO] Target frequency: 800000 KHz [INFO] Actual frequency:
> > > 787496 KHz [INFO] [INFO] Target frequency: 1000000 KHz [INFO]
> > > Actual frequency: 974996 KHz [INFO] [INFO] Target frequency:
> > > 1200000 KHz [INFO] Actual frequency: 1199995 KHz
> > >
> > > Regards,
> > > Biju
> > >
> >
>
>
> --
> Gr{oetje,eeting}s,
>
> Geert
>
> --
> Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-
> m68k.org
>
> In personal conversations with technical people, I call myself a hacker. But
> when I'm talking to journalists I just say "programmer" or something like that.
> -- Linus Torvalds
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