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cpufreq/amd-pstate: Remove the defensive check for bios_min_perf

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Initialization of bios_min_perf (BIOS Requested CPU Min Freq.) only
succeeds when the driver init finds the CPPC_REQ MSRs to have all 0s
except for MIN_PERF bits.

A kexec puts the driver through the suspend path which, although resets
the min_perf back to bios_min_perf, keeps the rest of the CPPR_REQ
intact with the last value at the time of suspend.

The defensive check for bios_min_perf exists to prevent the min perf
from last CPPC_REQ being incorrectly considered as bios_min_perf when
a kexec switches from an older kernel running the version of driver
which is not aware of bios_min_perf to a newer one.

This scenario is extremely unlikely and Mario suggested it is better to
simplify the initialization rather than complicating the suspend resume
paths.

Drop the defensive check for bios_min_perf initialization and add a
debug message to dump the BIOS Requested Min Freq. to console leaving
enough breadcrumbs for debug if a situation so arises.

Suggested-by: Mario Limonciello <mario.limonciello@amd.com>
Reviewed-by: Mario Limonciello (AMD) <superm1@kernel.org>
Signed-off-by: K Prateek Nayak <kprateek.nayak@amd.com>
Link: https://lore.kernel.org/r/20260727072056.1248-3-kprateek.nayak@amd.com
Signed-off-by: Mario Limonciello <superm1@kernel.org>
This commit is contained in:
K Prateek Nayak
2026-07-27 07:20:49 +00:00
committed by Mario Limonciello
parent 5c3ecf36d2
commit 0e85027801
1 changed files with 8 additions and 11 deletions
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19
drivers/cpufreq/amd-pstate.c
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@@ -462,7 +462,6 @@ static int msr_init_perf(struct amd_cpudata *cpudata)
{
union perf_cached perf = READ_ONCE(cpudata->perf);
u64 cap1, numerator, cppc_req;
u8 min_perf;
int ret = rdmsrq_safe_on_cpu(cpudata->cpu, MSR_AMD_CPPC_CAP1,
&cap1);
@@ -478,16 +477,6 @@ static int msr_init_perf(struct amd_cpudata *cpudata)
return ret;
WRITE_ONCE(cpudata->cppc_req_cached, cppc_req);
min_perf = FIELD_GET(AMD_CPPC_MIN_PERF_MASK, cppc_req);
/*
* Clear out the min_perf part to check if the rest of the MSR is 0, if yes, this is an
* indication that the min_perf value is the one specified through the BIOS option
*/
cppc_req &= ~(AMD_CPPC_MIN_PERF_MASK);
if (!cppc_req)
perf.bios_min_perf = min_perf;
perf.highest_perf = numerator;
perf.max_limit_perf = numerator;
@@ -495,6 +484,7 @@ static int msr_init_perf(struct amd_cpudata *cpudata)
perf.nominal_perf = FIELD_GET(AMD_CPPC_NOMINAL_PERF_MASK, cap1);
perf.lowest_nonlinear_perf = FIELD_GET(AMD_CPPC_LOWNONLIN_PERF_MASK, cap1);
perf.lowest_perf = FIELD_GET(AMD_CPPC_LOWEST_PERF_MASK, cap1);
perf.bios_min_perf = FIELD_GET(AMD_CPPC_MIN_PERF_MASK, cppc_req);
WRITE_ONCE(cpudata->perf, perf);
WRITE_ONCE(cpudata->prefcore_ranking, FIELD_GET(AMD_CPPC_HIGHEST_PERF_MASK, cap1));
WRITE_ONCE(cpudata->floor_perf_cnt, FIELD_GET(AMD_CPPC_FLOOR_PERF_CNT_MASK, cap1));
@@ -1044,6 +1034,13 @@ static int amd_pstate_init_freq(struct amd_cpudata *cpudata)
return -EINVAL;
}
if (perf.bios_min_perf) {
u32 bios_min_freq = perf_to_freq(perf, cpudata->nominal_freq, perf.bios_min_perf);
pr_debug("Found Requested CPU Min Frequency of %uKHz on CPU%d\n",
bios_min_freq, cpudata->cpu);
}
return 0;
}