linux-kernel - [PATCH] cpufreq/amd-pstate: Fix the clamping of perf values

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Message-ID: <20250222033221.554976-1-dhananjay.ugwekar@amd.com>
Date: Sat, 22 Feb 2025 03:32:22 +0000
From: Dhananjay Ugwekar <dhananjay.ugwekar@....com>
To: <gautham.shenoy@....com>, <mario.limonciello@....com>,
	<perry.yuan@....com>, <rafael@...nel.org>, <viresh.kumar@...aro.org>
CC: <linux-pm@...r.kernel.org>, <linux-kernel@...r.kernel.org>, "Dhananjay
 Ugwekar" <dhananjay.ugwekar@....com>
Subject: [PATCH] cpufreq/amd-pstate: Fix the clamping of perf values

The clamping in freq_to_perf() is broken right now, as we first typecast
(read wraparound) the overflowing value into a u8 and then clamp it down.
So, use a u32 to store the >255 value in certain edge cases and then clamp
it down into a u8.

Also, use a "explicit typecast + clamp" instead of just a "clamp_t" as the
latter typecasts first and then clamps between the limits, which defeats
our purpose.

Fixes: 305621eb6a8b ("cpufreq/amd-pstate: Modularize perf<->freq conversion")
Signed-off-by: Dhananjay Ugwekar <dhananjay.ugwekar@....com>
---
 drivers/cpufreq/amd-pstate.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/cpufreq/amd-pstate.c b/drivers/cpufreq/amd-pstate.c
index 9ab95ec1f828..4705a644db6d 100644
--- a/drivers/cpufreq/amd-pstate.c
+++ b/drivers/cpufreq/amd-pstate.c
@@ -144,10 +144,10 @@ static struct quirk_entry quirk_amd_7k62 = {
 
 static inline u8 freq_to_perf(struct amd_cpudata *cpudata, unsigned int freq_val)
 {
-	u8 perf_val = DIV_ROUND_UP_ULL((u64)freq_val * cpudata->nominal_perf,
+	u32 perf_val = DIV_ROUND_UP_ULL((u64)freq_val * cpudata->nominal_perf,
 					cpudata->nominal_freq);
 
-	return clamp_t(u8, perf_val, cpudata->lowest_perf, cpudata->highest_perf);
+	return (u8)clamp(perf_val, cpudata->lowest_perf, cpudata->highest_perf);
 }
 
 static inline u32 perf_to_freq(struct amd_cpudata *cpudata, u8 perf_val)
-- 
2.34.1