On 04.09.2025 08:35, Penny Zheng wrote:
> @@ -50,10 +139,333 @@ int __init amd_cppc_cmdline_parse(const char *s, const
> char *e)
> return 0;
> }
>
> +/*
> + * If CPPC lowest_freq and nominal_freq registers are exposed then we can
> + * use them to convert perf to freq and vice versa. The conversion is
> + * extrapolated as an linear function passing by the 2 points:
> + * - (Low perf, Low freq)
> + * - (Nominal perf, Nominal freq)
> + * Parameter freq is always in kHz.
> + */
> +static int amd_cppc_khz_to_perf(const struct amd_cppc_drv_data *data,
> + unsigned int freq, uint8_t *perf)
> +{
> + const struct xen_processor_cppc *cppc_data = data->cppc_data;
> + unsigned int mul, div;
> + int offset = 0, res;
> +
> + if ( cppc_data->cpc.lowest_mhz &&
> + data->caps.nominal_perf > data->caps.lowest_perf &&
> + cppc_data->cpc.nominal_mhz > cppc_data->cpc.lowest_mhz )
> + {
> + mul = data->caps.nominal_perf - data->caps.lowest_perf;
> + div = cppc_data->cpc.nominal_mhz - cppc_data->cpc.lowest_mhz;
> +
> + /*
> + * We don't need to convert to kHz for computing offset and can
> + * directly use nominal_mhz and lowest_mhz as the division
> + * will remove the frequency unit.
> + */
> + offset = data->caps.nominal_perf -
> + (mul * cppc_data->cpc.nominal_mhz) / div;
> + }
> + else
> + {
> + /* Read Processor Max Speed(MHz) as anchor point */
> + mul = data->caps.highest_perf;
> + div = this_cpu(pxfreq_mhz);
How do you know you ever initialized this instance of the per-CPU variable?
amd_cppc_init_msrs() may never have run for this particular CPU.
> +static int cf_check amd_cppc_cpufreq_target(struct cpufreq_policy *policy,
> + unsigned int target_freq,
> + unsigned int relation)
> +{
> + struct amd_cppc_drv_data *data = policy->u.amd_cppc;
> + uint8_t des_perf;
> + int res;
> +
> + if ( unlikely(!target_freq) )
> + return 0;
> +
> + res = amd_cppc_khz_to_perf(data, target_freq, &des_perf);
> + if ( res )
> + return res;
> +
> + /*
> + * Having a performance level lower than the lowest nonlinear
> + * performance level, such as, lowest_perf <= perf <=
> lowest_nonliner_perf,
> + * may actually cause an efficiency penalty, So when deciding the
> min_perf
> + * value, we prefer lowest nonlinear performance over lowest performance.
> + */
> + amd_cppc_write_request(policy->cpu, data,
> data->caps.lowest_nonlinear_perf,
> + des_perf, data->caps.highest_perf,
> + /* Pre-defined BIOS value for passive mode */
> + per_cpu(epp_init, policy->cpu));
This may access per-CPU data of an offline CPU.
Jan
