[PATCH v2 2/9] cpufreq/amd-pstate: Remove the defensive check for bios_min_perf

[K Prateek Nayak]

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@xxxxxxx>
Signed-off-by: K Prateek Nayak <kprateek.nayak@xxxxxxx>
---
Changelog rfc v1..v2:

o Reworked based on review comments from Mario.
---
 drivers/cpufreq/amd-pstate.c | 19 ++++++++-----------
 1 file changed, 8 insertions(+), 11 deletions(-)

diff --git a/drivers/cpufreq/amd-pstate.c b/drivers/cpufreq/amd-pstate.c
index 1157f05df10f..02308e95636e 100644
--- a/drivers/cpufreq/amd-pstate.c
+++ b/drivers/cpufreq/amd-pstate.c
@@ -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));
@@ -1043,6 +1033,13 @@ 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 %uMHz on CPU%d\n",
+			 bios_min_freq, cpudata->cpu);
+	}
+
 	return 0;
 }
 
-- 
2.34.1