Re: [PATCH] cpufreq: CPPC: Return desired perf in ->get() if feedback counters are 0

Jie Zhan
2024-08-21T08:27:51Z

cc linux-arm-kernel

On 19/08/2024 11:51, Jie Zhan wrote:
> The CPPC performance feedback counters could return 0 when the target cpu
> is in a deep idle state (e.g. powered off) and those counters are not
> powered. cppc_cpufreq_get_rate() returns 0 in this case, triggering two
> problems:
>
> 1. cpufreq_online() gets a false error and doesn't generate a cpufreq
> policy, which happens in cpufreq_add_dev() when a new cpu device is added.
> 2. 'cpuinfo_cur_freq' shows '<unknown>'
>
> Don't take it as an error and return the frequency corresponding to the
> desired perf when the feedback counters are 0.
>
> Fixes: 6a4fec4f6d30 ("cpufreq: cppc: cppc_cpufreq_get_rate() returns zero in all error cases.")
> Signed-off-by: Jie Zhan <zhanjie9@hisilicon.com>
> ---
> drivers/cpufreq/cppc_cpufreq.c | 11 +++++++++--
> 1 file changed, 9 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/cpufreq/cppc_cpufreq.c b/drivers/cpufreq/cppc_cpufreq.c
> index bafa32dd375d..1c5eb12c1a5a 100644
> --- a/drivers/cpufreq/cppc_cpufreq.c
> +++ b/drivers/cpufreq/cppc_cpufreq.c
> @@ -748,18 +748,25 @@ static unsigned int cppc_cpufreq_get_rate(unsigned int cpu)
>
> ret = cppc_get_perf_ctrs(cpu, &fb_ctrs_t0);
> if (ret)
> - return 0;
> + goto out_err;
>
> udelay(2); /* 2usec delay between sampling */
>
> ret = cppc_get_perf_ctrs(cpu, &fb_ctrs_t1);
> if (ret)
> - return 0;
> + goto out_err;
>
> delivered_perf = cppc_perf_from_fbctrs(cpu_data, &fb_ctrs_t0,
> &fb_ctrs_t1);
>
> return cppc_perf_to_khz(&cpu_data->perf_caps, delivered_perf);
> +
> +out_err:
> + if (ret == -EFAULT)
> + return cppc_perf_to_khz(&cpu_data->perf_caps,
> + cpu_data->perf_ctrls.desired_perf);
> +
> + return 0;
> }
>
> static int cppc_cpufreq_set_boost(struct cpufreq_policy *policy, int state)