linux-kernel - [PATCH v2] Add hardcoded crystal clock for KabyLake

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Message-Id: <20221018190124.v2.1.I918ccc908c5c836c1e21e01d2cf6f59b0157bcc3@changeid>
Date:   Tue, 18 Oct 2022 19:01:32 +0000
From:   Rishabh Agrawal <rishabhagr@...omium.org>
To:     LKML <linux-kernel@...r.kernel.org>, len.brown@...el.com,
        drake@...lessm.com, rafael.j.wysocki@...el.com, mingo@...hat.com,
        tglx@...utronix.de
Cc:     vaibhav.shankar@...el.com, biernacki@...gle.com,
        zwisler@...gle.com, mattedavis@...gle.com,
        Rishabh Agrawal <rishabhagr@...omium.org>,
        Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Feng Tang <feng.tang@...el.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        Peter Zijlstra <peterz@...radead.org>, x86@...nel.org
Subject: [PATCH v2] Add hardcoded crystal clock for KabyLake

Set KabyLake crystal clock manually since the TSC calibration is off
by 0.5%. All the tests that are based on the timer/clock will fail in
this case.

The HPET has been disabled by upstream due to PC10 issue causing the
3 hatch devices, dratini, jinlon, and kohaku to not calibrate the clock
precisely. These 3 devices are KabyLake devices. Intel team has verified
that all KBL devices have 24.0 MHz clock frequency, therefore this
change is valid.

Signed-off-by: Rishabh Agrawal <rishabhagr@...omium.org>
---

Changes in v2:
  - Adding Thomas Gleixner, Daniel Drake, Rafael Wysocki, Len brown and Ingo to review since you worked on this.

 arch/x86/kernel/tsc.c | 17 ++++++++++++++---
 1 file changed, 14 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c
index cafacb2e58cc..63a06224fa48 100644
--- a/arch/x86/kernel/tsc.c
+++ b/arch/x86/kernel/tsc.c
@@ -644,10 +644,21 @@ unsigned long native_calibrate_tsc(void)
 	 * Denverton SoCs don't report crystal clock, and also don't support
 	 * CPUID.0x16 for the calculation below, so hardcode the 25MHz crystal
 	 * clock.
+	 *
+	 * Intel KabyLake devices' clocks are off by 0.5% when using the below
+	 * calculation, so hardcode 24.0 MHz crystal clock.
 	 */
-	if (crystal_khz == 0 &&
-			boot_cpu_data.x86_model == INTEL_FAM6_ATOM_GOLDMONT_D)
-		crystal_khz = 25000;
+	if (crystal_khz == 0) {
+		switch (boot_cpu_data.x86_model) {
+		case INTEL_FAM6_ATOM_GOLDMONT_D:
+			crystal_khz = 25000;
+			break;
+		case INTEL_FAM6_KABYLAKE_L:
+			crystal_khz = 24000;
+			break;
+		}
+
+	}
 
 	/*
 	 * TSC frequency reported directly by CPUID is a "hardware reported"
-- 
2.38.0.413.g74048e4d9e-goog