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

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Date:   Fri, 06 Aug 2021 12:12:42 +0530
From:   Sibi Sankar <sibis@...eaurora.org>
To:     Stephen Boyd <swboyd@...omium.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

On 2021-08-05 23:55, Stephen Boyd wrote:
> 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?

https://lore.kernel.org/lkml/20190814152116.GB28465@jcrouse1-lnx.qualcomm.com/

GPU was supposed to be one of the
other clients that would vote for
l3.

> 
>> 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.

Taniya probably would know more
about the history behind the change.
I'll dig up more info regarding ^^
and update the thread.


-- 
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