Re: [PATCH v3 1/2] cpufreq: acpi-cpufreq: fix P-state index mismatch in extract_io()

[Zhongqiu Han <zhongqiu.han@oss.qualcomm.com>]

On 8/20/2026 10:07 AM, lirongqing wrote:
> From: Li RongQing <lirongqing@baidu.com>
> 
> When policy->freq_table is built in acpi_cpufreq_cpu_init(), entries
> with duplicate frequencies are skipped. For each remaining entry,

To be precise for applying if needed.

"entries with duplicate frequencies are skipped.

-->

entries that are not lower in frequency than the previous one are
skipped."


> freq_table[].driver_data stores the original ACPI P-state index, so the
> index space of freq_table no longer matches perf->states[].
> 
> extract_io() currently walks perf->states[] with index i and uses the
> same i to index policy->freq_table[i]. When duplicate frequencies
> exist, this can associate a P-state status with the frequency of a
> different P-state. It can also access an invalid or sentinel entry in
> freq_table when the number of entries in perf->states[] is greater than
> the number of entries remaining in the frequency table.
> 
> extract_io() is used on ACPI_ADR_SPACE_SYSTEM_IO platforms by the
> frequency verification path, which is enabled by the
> acpi_pstate_strict module parameter. With the mismatched lookup,
> check_freqs() can fail to match the frequency of the P-state that
> drv_write() has already programmed. It then retries the check for all
> iterations before returning -EAGAIN, 

Small nit, just for applying if needed.

"It then retries the check for all iterations before returning -EAGAIN,"

-->

"It then sleeps through all 100 iterations - at least
~1 ms of usleep_range() plus 100 cross-CPU calls and I/O port reads, all
with policy->rwsem held, and .target_index() returns -EAGAIN,"


leaving perf->state at its
> previous value while the hardware is running at the newly requested
> P-state.
> 
> The cpufreq core consequently keeps policy->cur at the old frequency.
> Since __cpufreq_driver_target() returns early when the requested
> frequency equals policy->cur, the driver is not called again for that
> frequency and the control register is not rewritten. The hardware can
> therefore remain at a frequency that differs from the frequency known
> to the cpufreq core.
> 
> Fix this by iterating over policy->freq_table and using
> pos->driver_data as the original ACPI P-state index when accessing
> perf->states[], as extract_msr() already does.
> 
> Fixes: fe27cb358835 ("[CPUFREQ][2/8] acpi: reorganize code to make MSR support addition easier")
> Signed-off-by: Li RongQing <lirongqing@baidu.com>

Reviewed-by: Zhongqiu Han <zhongqiu.han@oss.qualcomm.com>

> ---
>   drivers/cpufreq/acpi-cpufreq.c | 9 ++++-----
>   1 file changed, 4 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/cpufreq/acpi-cpufreq.c b/drivers/cpufreq/acpi-cpufreq.c
> index 10ea603..a797bb2 100644
> --- a/drivers/cpufreq/acpi-cpufreq.c
> +++ b/drivers/cpufreq/acpi-cpufreq.c
> @@ -197,14 +197,13 @@ static unsigned extract_io(struct cpufreq_policy *policy, u32 value)
>   {
>   	struct acpi_cpufreq_data *data = policy->driver_data;
>   	struct acpi_processor_performance *perf;
> -	int i;
> +	struct cpufreq_frequency_table *pos;
>   
>   	perf = to_perf_data(data);
>   
> -	for (i = 0; i < perf->state_count; i++) {
> -		if (value == perf->states[i].status)
> -			return policy->freq_table[i].frequency;
> -	}
> +	cpufreq_for_each_entry(pos, policy->freq_table)
> +		if (value == perf->states[pos->driver_data].status)
> +			return pos->frequency;
>   	return 0;
>   }
>   


-- 
Thx and BRs,
Zhongqiu Han