Re: [PATCH v6 4/5] cpufreq: qcom: Update the bandwidth levels on frequency change

[Sibi Sankar <sibis@codeaurora.org>]

Hey Matthias,
Thanks for taking time to review
the series.

On 2020-06-15 22:55, Matthias Kaehlcke wrote:
> Hi Sibi,
> 
> On Sat, Jun 06, 2020 at 03:03:31AM +0530, Sibi Sankar wrote:
>> Add support to parse optional OPP table attached to the cpu node when
>> the OPP bandwidth values are populated. This allows for scaling of
>> DDR/L3 bandwidth levels with frequency change.
>> 
>> Signed-off-by: Sibi Sankar <sibis@codeaurora.org>
>> ---
>> 
>> v6:
>>  * Add global flag to distinguish between voltage update and opp add.
>>    Use the same flag before trying to scale ddr/l3 bw [Viresh]
>>  * Use dev_pm_opp_find_freq_ceil to grab all opps [Viresh]
>>  * Move dev_pm_opp_of_find_icc_paths into probe [Viresh]
>> 
>> v5:
>>  * Use dev_pm_opp_adjust_voltage instead [Viresh]
>>  * Misc cleanup
>> 
>> v4:
>>  * Split fast switch disable into another patch [Lukasz]
>> 
>>  drivers/cpufreq/qcom-cpufreq-hw.c | 82 
>> ++++++++++++++++++++++++++++++-
>>  1 file changed, 80 insertions(+), 2 deletions(-)
>> 
>> diff --git a/drivers/cpufreq/qcom-cpufreq-hw.c 
>> b/drivers/cpufreq/qcom-cpufreq-hw.c
>> index fc92a8842e252..8fa6ab6e0e4b6 100644
>> --- a/drivers/cpufreq/qcom-cpufreq-hw.c
>> +++ b/drivers/cpufreq/qcom-cpufreq-hw.c
>> @@ -6,6 +6,7 @@
>>  #include <linux/bitfield.h>
>>  #include <linux/cpufreq.h>
>>  #include <linux/init.h>
>> +#include <linux/interconnect.h>
>>  #include <linux/kernel.h>
>>  #include <linux/module.h>
>>  #include <linux/of_address.h>
>> @@ -30,6 +31,48 @@
>> 
>>  static unsigned long cpu_hw_rate, xo_rate;
>>  static struct platform_device *global_pdev;
>> +static bool icc_scaling_enabled;
> 
> It seem you rely on 'icc_scaling_enabled' to be initialized to 'false'.
> This works during the first initialization, but not if the 'device' is
> unbound/rebound. In theory things shouldn't be different in a succesive

yes it shouldn't but sure I'll set
it to false along the way.

> initialization, however for robustness the variable should be 
> explicitly
> set to 'false' somewhere in the code path (_probe(), _read_lut(), ...).

> 
>> +static int qcom_cpufreq_set_bw(struct cpufreq_policy *policy,
>> +			       unsigned long freq_khz)
>> +{
>> +	unsigned long freq_hz = freq_khz * 1000;
>> +	struct dev_pm_opp *opp;
>> +	struct device *dev;
>> +	int ret;
>> +
>> +	dev = get_cpu_device(policy->cpu);
>> +	if (!dev)
>> +		return -ENODEV;
>> +
>> +	opp = dev_pm_opp_find_freq_exact(dev, freq_hz, true);
>> +	if (IS_ERR(opp))
>> +		return PTR_ERR(opp);
>> +
>> +	ret = dev_pm_opp_set_bw(dev, opp);
>> +	dev_pm_opp_put(opp);
>> +	return ret;
>> +}
>> +
>> +static int qcom_cpufreq_update_opp(struct device *cpu_dev,
>> +				   unsigned long freq_khz,
>> +				   unsigned long volt)
>> +{
>> +	unsigned long freq_hz = freq_khz * 1000;
>> +	int ret;
>> +
>> +	/* Skip voltage update if the opp table is not available */
>> +	if (!icc_scaling_enabled)
>> +		return dev_pm_opp_add(cpu_dev, freq_hz, volt);
>> +
>> +	ret = dev_pm_opp_adjust_voltage(cpu_dev, freq_hz, volt, volt, volt);
>> +	if (ret) {
>> +		dev_err(cpu_dev, "Voltage update failed freq=%ld\n", freq_khz);
>> +		return ret;
>> +	}
>> +
>> +	return dev_pm_opp_enable(cpu_dev, freq_hz);
>> +}
>> 
>>  static int qcom_cpufreq_hw_target_index(struct cpufreq_policy 
>> *policy,
>>  					unsigned int index)
>> @@ -39,6 +82,9 @@ static int qcom_cpufreq_hw_target_index(struct 
>> cpufreq_policy *policy,
>> 
>>  	writel_relaxed(index, perf_state_reg);
>> 
>> +	if (icc_scaling_enabled)
>> +		qcom_cpufreq_set_bw(policy, freq);
>> +
>>  	arch_set_freq_scale(policy->related_cpus, freq,
>>  			    policy->cpuinfo.max_freq);
>>  	return 0;
>> @@ -89,11 +135,31 @@ static int qcom_cpufreq_hw_read_lut(struct device 
>> *cpu_dev,
>>  	u32 data, src, lval, i, core_count, prev_freq = 0, freq;
>>  	u32 volt;
>>  	struct cpufreq_frequency_table	*table;
>> +	struct dev_pm_opp *opp;
>> +	unsigned long rate;
>> +	int ret;
>> 
>>  	table = kcalloc(LUT_MAX_ENTRIES + 1, sizeof(*table), GFP_KERNEL);
>>  	if (!table)
>>  		return -ENOMEM;
>> 
>> +	ret = dev_pm_opp_of_add_table(cpu_dev);
>> +	if (!ret) {
>> +		/* Disable all opps and cross-validate against LUT */
> 
> nit: IIUC the cross-validation doesn't happen in this branch, so the
> comment is a bit misleading. Maybe change it to "Disable all opps to
> cross-validate against the LUT {below,later}".

sure will re-word it.

> 
>> +		icc_scaling_enabled = true;
>> +		for (rate = 0; ; rate++) {
>> +			opp = dev_pm_opp_find_freq_ceil(cpu_dev, &rate);
>> +			if (IS_ERR(opp))
>> +				break;
>> +
>> +			dev_pm_opp_put(opp);
>> +			dev_pm_opp_disable(cpu_dev, rate);
>> +		}
>> +	} else if (ret != -ENODEV) {
>> +		dev_err(cpu_dev, "Invalid opp table in device tree\n");
>> +		return ret;
>> +	}
>> +
>>  	for (i = 0; i < LUT_MAX_ENTRIES; i++) {
>>  		data = readl_relaxed(base + REG_FREQ_LUT +
>>  				      i * LUT_ROW_SIZE);
>> @@ -112,7 +178,7 @@ static int qcom_cpufreq_hw_read_lut(struct device 
>> *cpu_dev,
>> 
>>  		if (freq != prev_freq && core_count != LUT_TURBO_IND) {
>>  			table[i].frequency = freq;
>> -			dev_pm_opp_add(cpu_dev, freq * 1000, volt);
>> +			qcom_cpufreq_update_opp(cpu_dev, freq, volt);
> 
> This is the cross-validation mentioned above, right? Shouldn't it 
> include
> a check of the return value?

Yes, this is the cross-validation step,
we adjust the voltage if opp-tables are
present/added successfully and enable
them, else we would just do a add opp.
We don't want to exit early on a single
opp failure. We will error out a bit
later if the opp-count ends up to be
zero.

> 
>>  			dev_dbg(cpu_dev, "index=%d freq=%d, core_count %d\n", i,
>>  				freq, core_count);
>>  		} else if (core_count == LUT_TURBO_IND) {
>> @@ -133,7 +199,8 @@ static int qcom_cpufreq_hw_read_lut(struct device 
>> *cpu_dev,
>>  			if (prev->frequency == CPUFREQ_ENTRY_INVALID) {
>>  				prev->frequency = prev_freq;
>>  				prev->flags = CPUFREQ_BOOST_FREQ;
>> -				dev_pm_opp_add(cpu_dev,	prev_freq * 1000, volt);
>> +				qcom_cpufreq_update_opp(cpu_dev, prev_freq,
>> +							volt);
> 
> ditto
> 
> nit: with the updated max line length it isn't necessary anymore to 
> break
> this into multiple lines
> (https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/scripts/checkpatch.pl?h=v5.8-rc1#n54),
> though the coding style still has the old limit.

yeah I'll expand it.

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