[Devel] [PATCH RH7 1/2] ms/cpufreq: intel_pstate: Add reasons for failure and debug messages

[Evgenii Shatokhin]

From: Erwan Velu <e.velu at criteo.com>

The init code path has several exceptions where the driver can
decide not to load.

As CONFIG_X86_INTEL_PSTATE is generally set to Y, the return code is
not reachable.  The initialization code is neither verbose of the
reason why it did choose to prematurely exit, so it is difficult for
a user to determine, on a given platform, why the driver didn't load
properly.

This patch is about reporting to the user the reason/context of why
the driver failed to load.  That is a precious hint when debugging
a platform.

Signed-off-by: Erwan Velu <e.velu at criteo.com>
[ rjw: Subject & changelog, minor fixups ]
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki at intel.com>

Commit 076b862c7e4409d2dcacfda19f7eaf8d07ab9200 in the mainline kernel.
Added in the scope of https://jira.sw.ru/browse/PSBM-126007

Signed-off-by: Evgenii Shatokhin <eshatokhin at virtuozzo.com>
---
 drivers/cpufreq/intel_pstate.c | 27 +++++++++++++++++++++------
 1 file changed, 21 insertions(+), 6 deletions(-)

diff --git a/drivers/cpufreq/intel_pstate.c b/drivers/cpufreq/intel_pstate.c
index d4825dce5258..4283d1bc0363 100644
--- a/drivers/cpufreq/intel_pstate.c
+++ b/drivers/cpufreq/intel_pstate.c
@@ -2409,6 +2409,7 @@ static bool intel_pstate_no_acpi_pss(void)
 		kfree(pss);
 	}
 
+	pr_debug("ACPI _PSS not found\n");
 	return true;
 }
 
@@ -2419,9 +2420,14 @@ static bool __init intel_pstate_no_acpi_pcch(void)
 
 	status = acpi_get_handle(NULL, "\\_SB", &handle);
 	if (ACPI_FAILURE(status))
-		return true;
+		goto not_found;
+
+	if (acpi_has_method(handle, "PCCH"))
+		return false;
 
-	return !acpi_has_method(handle, "PCCH");
+not_found:
+	pr_debug("ACPI PCCH not found\n");
+	return true;
 }
 
 static bool intel_pstate_has_acpi_ppc(void)
@@ -2436,6 +2442,7 @@ static bool intel_pstate_has_acpi_ppc(void)
 		if (acpi_has_method(pr->handle, "_PPC"))
 			return true;
 	}
+	pr_debug("ACPI _PPC not found\n");
 	return false;
 }
 
@@ -2481,8 +2488,10 @@ static bool intel_pstate_platform_pwr_mgmt_exists(void)
 	id = x86_match_cpu(intel_pstate_cpu_oob_ids);
 	if (id) {
 		rdmsrl(MSR_MISC_PWR_MGMT, misc_pwr);
-		if ( misc_pwr & (1 << 8))
+		if (misc_pwr & (1 << 8)) {
+			pr_debug("Bit 8 in the MISC_PWR_MGMT MSR set\n");
 			return true;
+		}
 	}
 
 	if (acpi_disabled ||
@@ -2550,22 +2559,28 @@ static int __init intel_pstate_init(void)
 		const struct x86_cpu_id *id;
 
 		id = x86_match_cpu(intel_pstate_cpu_ids);
-		if (!id)
+		if (!id) {
+			pr_info("CPU ID not supported\n");
 			return -ENODEV;
+		}
 
 		copy_cpu_funcs((struct pstate_funcs *)id->driver_data);
 	}
 
-	if (intel_pstate_msrs_not_valid())
+	if (intel_pstate_msrs_not_valid()) {
+		pr_info("Invalid MSRs\n");
 		return -ENODEV;
+	}
 
 hwp_cpu_matched:
 	/*
 	 * The Intel pstate driver will be ignored if the platform
 	 * firmware has its own power management modes.
 	 */
-	if (intel_pstate_platform_pwr_mgmt_exists())
+	if (intel_pstate_platform_pwr_mgmt_exists()) {
+		pr_info("P-states controlled by the platform\n");
 		return -ENODEV;
+	}
 
 	if (!hwp_active && hwp_only)
 		return -ENOTSUPP;
-- 
2.27.0