linux-kernel - Re: [PATCH 2/4] cpufreq: qcom: Re-arrange register offsets to support per core L3 DCVS

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Date:   Thu, 5 Aug 2021 11:25:36 -0700
From:   Stephen Boyd <swboyd@...omium.org>
To:     Sibi Sankar <sibis@...eaurora.org>
Cc:     bjorn.andersson@...aro.org, mka@...omium.org, robh+dt@...nel.org,
        viresh.kumar@...aro.org, agross@...nel.org, rjw@...ysocki.net,
        linux-arm-msm@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
        dianders@...omium.org, tdas@...eaurora.org
Subject: Re: [PATCH 2/4] cpufreq: qcom: Re-arrange register offsets to support
 per core L3 DCVS

Quoting Sibi Sankar (2021-08-05 10:47:20)
> Stephen,
>
> Thanks for taking time to review
> the series.
>
> On 2021-08-05 00:31, Stephen Boyd wrote:
> > Quoting Sibi Sankar (2021-07-29 11:04:43)
> >> Qualcomm SoCs (starting with SM8350) support per core voting for L3
> >> cache
> >> frequency.
> >
> > And the L3 cache frequency voting code can't be put into this cpufreq
> > driver?
>
> Yes, it could have gone either into
> the cpufreq driver or l3 interconnect
> provider driver. Taniya/Odelu preferred
> the latter, because of the need for other
> clients to vote for l3 frequencies in
> the future.

What other clients are those?

> The other option to prevent
> register re-arrangement would involve
> using syscons from the cpufreq node, which
> really wasn't necessary since there
> wasn't any register overlap between the
> two drivers.

Let's not do that.

>
> >
> >> So, re-arrange the cpufreq register offsets to allow access for
> >> the L3 interconnect to implement per core control. Also prevent
> >> binding
> >> breakage caused by register offset shuffling by using the
> >> SM8250/SM8350
> >> EPSS compatible.
> >>
> >> Fixes: 7dbd121a2c58 ("arm64: dts: qcom: sc7280: Add cpufreq hw node")
> >> Signed-off-by: Sibi Sankar <sibis@...eaurora.org>
> >> ---
> >>  drivers/cpufreq/qcom-cpufreq-hw.c | 23 +++++++++++++++++++----
> >>  1 file changed, 19 insertions(+), 4 deletions(-)
> >>
> >> diff --git a/drivers/cpufreq/qcom-cpufreq-hw.c
> >> b/drivers/cpufreq/qcom-cpufreq-hw.c
> >> index f86859bf76f1..74ef3b38343b 100644
> >> --- a/drivers/cpufreq/qcom-cpufreq-hw.c
> >> +++ b/drivers/cpufreq/qcom-cpufreq-hw.c
> >> @@ -28,6 +28,7 @@ struct qcom_cpufreq_soc_data {
> >>         u32 reg_volt_lut;
> >>         u32 reg_perf_state;
> >>         u8 lut_row_size;
> >> +       bool skip_enable;
> >>  };
> >>
> >>  struct qcom_cpufreq_data {
> >> @@ -257,19 +258,31 @@ static const struct qcom_cpufreq_soc_data
> >> qcom_soc_data = {
> >>         .reg_volt_lut = 0x114,
> >>         .reg_perf_state = 0x920,
> >>         .lut_row_size = 32,
> >> +       .skip_enable = false,
> >>  };
> >>
> >>  static const struct qcom_cpufreq_soc_data epss_soc_data = {
> >> +       .reg_freq_lut = 0x0,
> >> +       .reg_volt_lut = 0x100,
> >> +       .reg_perf_state = 0x220,
> >> +       .lut_row_size = 4,
> >> +       .skip_enable = true,
> >> +};
> >> +
> >> +static const struct qcom_cpufreq_soc_data epss_sm8250_soc_data = {
> >>         .reg_enable = 0x0,
> >>         .reg_freq_lut = 0x100,
> >>         .reg_volt_lut = 0x200,
> >>         .reg_perf_state = 0x320,
> >>         .lut_row_size = 4,
> >> +       .skip_enable = false,
> >>  };
> >>
> >>  static const struct of_device_id qcom_cpufreq_hw_match[] = {
> >>         { .compatible = "qcom,cpufreq-hw", .data = &qcom_soc_data },
> >>         { .compatible = "qcom,cpufreq-epss", .data = &epss_soc_data },
> >> +       { .compatible = "qcom,sm8250-cpufreq-epss", .data =
> >> &epss_sm8250_soc_data },
> >> +       { .compatible = "qcom,sm8350-cpufreq-epss", .data =
> >> &epss_sm8250_soc_data },
> >>         {}
> >>  };
> >>  MODULE_DEVICE_TABLE(of, qcom_cpufreq_hw_match);
> >> @@ -334,10 +347,12 @@ static int qcom_cpufreq_hw_cpu_init(struct
> >> cpufreq_policy *policy)
> >>         data->res = res;
> >>
> >>         /* HW should be in enabled state to proceed */
> >
> > It looks odd that we're no longer making sure that the clk domain is
> > enabled when we probe the driver. Why is that OK?
>
> On newer EPSS hw it's no longer
> required to perform the additional
> hw enable check. IIRC we don't do
> that on corresponding downstream
> kernels as well.

It's fairly clear that we no longer perform the additional check. The
question is why that's OK.