When the nominal_freq recorded by the kernel is equal to the lowest_freq,
and the frequency adjustment operation is triggered externally, there is
a logic error in cppc_perf_to_khz()/cppc_khz_to_perf(), resulting in perf
and khz conversion errors.

Fix this by adding the branch processing logic when nominal_freq is equal
to lowest_freq.

Fixes: ec1c7ad47664 ("cpufreq: CPPC: Fix performance/frequency conversion")
Signed-off-by: liwei <liwei728@huawei.com>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
---
v2:
    - Fix similar issue in cppc_khz_to_perf()
---
v3:
    - Add acked-by tag
---
 drivers/acpi/cppc_acpi.c | 22 +++++++++++++++++-----
 1 file changed, 17 insertions(+), 5 deletions(-)

diff --git a/drivers/acpi/cppc_acpi.c b/drivers/acpi/cppc_acpi.c
index b73b3aa92f3f..c3fc2c05d868 100644
--- a/drivers/acpi/cppc_acpi.c
+++ b/drivers/acpi/cppc_acpi.c
@@ -1916,9 +1916,15 @@ unsigned int cppc_perf_to_khz(struct cppc_perf_caps *caps, unsigned int perf)
 	u64 mul, div;
 
 	if (caps->lowest_freq && caps->nominal_freq) {
-		mul = caps->nominal_freq - caps->lowest_freq;
+		/* Avoid special case when nominal_freq is equal to lowest_freq */
+		if (caps->lowest_freq == caps->nominal_freq) {
+			mul = caps->nominal_freq;
+			div = caps->nominal_perf;
+		} else {
+			mul = caps->nominal_freq - caps->lowest_freq;
+			div = caps->nominal_perf - caps->lowest_perf;
+		}
 		mul *= KHZ_PER_MHZ;
-		div = caps->nominal_perf - caps->lowest_perf;
 		offset = caps->nominal_freq * KHZ_PER_MHZ -
 			 div64_u64(caps->nominal_perf * mul, div);
 	} else {
@@ -1939,11 +1945,17 @@ unsigned int cppc_khz_to_perf(struct cppc_perf_caps *caps, unsigned int freq)
 {
 	s64 retval, offset = 0;
 	static u64 max_khz;
-	u64  mul, div;
+	u64 mul, div;
 
 	if (caps->lowest_freq && caps->nominal_freq) {
-		mul = caps->nominal_perf - caps->lowest_perf;
-		div = caps->nominal_freq - caps->lowest_freq;
+		/* Avoid special case when nominal_freq is equal to lowest_freq */
+		if (caps->lowest_freq == caps->nominal_freq) {
+			mul = caps->nominal_perf;
+			div = caps->nominal_freq;
+		} else {
+			mul = caps->nominal_perf - caps->lowest_perf;
+			div = caps->nominal_freq - caps->lowest_freq;
+		}
 		/*
 		 * We don't need to convert to kHz for computing offset and can
 		 * directly use nominal_freq and lowest_freq as the div64_u64
-- 
2.25.1

On Thu, Oct 24, 2024 at 4:16 AM liwei <liwei728@huawei.com> wrote:
>
> When the nominal_freq recorded by the kernel is equal to the lowest_freq,
> and the frequency adjustment operation is triggered externally, there is
> a logic error in cppc_perf_to_khz()/cppc_khz_to_perf(), resulting in perf
> and khz conversion errors.
>
> Fix this by adding the branch processing logic when nominal_freq is equal
> to lowest_freq.
>
> Fixes: ec1c7ad47664 ("cpufreq: CPPC: Fix performance/frequency conversion")
> Signed-off-by: liwei <liwei728@huawei.com>
> Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
> ---
> v2:
>     - Fix similar issue in cppc_khz_to_perf()
> ---
> v3:
>     - Add acked-by tag
> ---
>  drivers/acpi/cppc_acpi.c | 22 +++++++++++++++++-----
>  1 file changed, 17 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/acpi/cppc_acpi.c b/drivers/acpi/cppc_acpi.c
> index b73b3aa92f3f..c3fc2c05d868 100644
> --- a/drivers/acpi/cppc_acpi.c
> +++ b/drivers/acpi/cppc_acpi.c
> @@ -1916,9 +1916,15 @@ unsigned int cppc_perf_to_khz(struct cppc_perf_caps *caps, unsigned int perf)
>         u64 mul, div;
>
>         if (caps->lowest_freq && caps->nominal_freq) {
> -               mul = caps->nominal_freq - caps->lowest_freq;
> +               /* Avoid special case when nominal_freq is equal to lowest_freq */
> +               if (caps->lowest_freq == caps->nominal_freq) {
> +                       mul = caps->nominal_freq;
> +                       div = caps->nominal_perf;
> +               } else {
> +                       mul = caps->nominal_freq - caps->lowest_freq;
> +                       div = caps->nominal_perf - caps->lowest_perf;
> +               }
>                 mul *= KHZ_PER_MHZ;
> -               div = caps->nominal_perf - caps->lowest_perf;
>                 offset = caps->nominal_freq * KHZ_PER_MHZ -
>                          div64_u64(caps->nominal_perf * mul, div);
>         } else {
> @@ -1939,11 +1945,17 @@ unsigned int cppc_khz_to_perf(struct cppc_perf_caps *caps, unsigned int freq)
>  {
>         s64 retval, offset = 0;
>         static u64 max_khz;
> -       u64  mul, div;
> +       u64 mul, div;
>
>         if (caps->lowest_freq && caps->nominal_freq) {
> -               mul = caps->nominal_perf - caps->lowest_perf;
> -               div = caps->nominal_freq - caps->lowest_freq;
> +               /* Avoid special case when nominal_freq is equal to lowest_freq */
> +               if (caps->lowest_freq == caps->nominal_freq) {
> +                       mul = caps->nominal_perf;
> +                       div = caps->nominal_freq;
> +               } else {
> +                       mul = caps->nominal_perf - caps->lowest_perf;
> +                       div = caps->nominal_freq - caps->lowest_freq;
> +               }
>                 /*
>                  * We don't need to convert to kHz for computing offset and can
>                  * directly use nominal_freq and lowest_freq as the div64_u64
> --

Applied as 6.12-rc material, thanks!