1 files changed, 236 insertions, 0 deletions
diff --git a/arch/x86/kernel/tsc_msr.c b/arch/x86/kernel/tsc_msr.c
new file mode 100644
index 0000000000..6555a857a1
--- /dev/null
+++ b/arch/x86/kernel/tsc_msr.c
@@ -0,0 +1,236 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * TSC frequency enumeration via MSR
+ *
+ * Copyright (C) 2013, 2018 Intel Corporation
+ * Author: Bin Gao <bin.gao@intel.com>
+ */
+
+#include <linux/kernel.h>
+#include <linux/thread_info.h>
+
+#include <asm/apic.h>
+#include <asm/cpu_device_id.h>
+#include <asm/intel-family.h>
+#include <asm/msr.h>
+#include <asm/param.h>
+#include <asm/tsc.h>
+
+#define MAX_NUM_FREQS	16 /* 4 bits to select the frequency */
+
+/*
+ * The frequency numbers in the SDM are e.g. 83.3 MHz, which does not contain a
+ * lot of accuracy which leads to clock drift. As far as we know Bay Trail SoCs
+ * use a 25 MHz crystal and Cherry Trail uses a 19.2 MHz crystal, the crystal
+ * is the source clk for a root PLL which outputs 1600 and 100 MHz. It is
+ * unclear if the root PLL outputs are used directly by the CPU clock PLL or
+ * if there is another PLL in between.
+ * This does not matter though, we can model the chain of PLLs as a single PLL
+ * with a quotient equal to the quotients of all PLLs in the chain multiplied.
+ * So we can create a simplified model of the CPU clock setup using a reference
+ * clock of 100 MHz plus a quotient which gets us as close to the frequency
+ * from the SDM as possible.
+ * For the 83.3 MHz example from above this would give us 100 MHz * 5 / 6 =
+ * 83 and 1/3 MHz, which matches exactly what has been measured on actual hw.
+ */
+#define TSC_REFERENCE_KHZ 100000
+
+struct muldiv {
+	u32 multiplier;
+	u32 divider;
+};
+
+/*
+ * If MSR_PERF_STAT[31] is set, the maximum resolved bus ratio can be
+ * read in MSR_PLATFORM_ID[12:8], otherwise in MSR_PERF_STAT[44:40].
+ * Unfortunately some Intel Atom SoCs aren't quite compliant to this,
+ * so we need manually differentiate SoC families. This is what the
+ * field use_msr_plat does.
+ */
+struct freq_desc {
+	bool use_msr_plat;
+	struct muldiv muldiv[MAX_NUM_FREQS];
+	/*
+	 * Some CPU frequencies in the SDM do not map to known PLL freqs, in
+	 * that case the muldiv array is empty and the freqs array is used.
+	 */
+	u32 freqs[MAX_NUM_FREQS];
+	u32 mask;
+};
+
+/*
+ * Penwell and Clovertrail use spread spectrum clock,
+ * so the freq number is not exactly the same as reported
+ * by MSR based on SDM.
+ */
+static const struct freq_desc freq_desc_pnw = {
+	.use_msr_plat = false,
+	.freqs = { 0, 0, 0, 0, 0, 99840, 0, 83200 },
+	.mask = 0x07,
+};
+
+static const struct freq_desc freq_desc_clv = {
+	.use_msr_plat = false,
+	.freqs = { 0, 133200, 0, 0, 0, 99840, 0, 83200 },
+	.mask = 0x07,
+};
+
+/*
+ * Bay Trail SDM MSR_FSB_FREQ frequencies simplified PLL model:
+ *  000:   100 *  5 /  6  =  83.3333 MHz
+ *  001:   100 *  1 /  1  = 100.0000 MHz
+ *  010:   100 *  4 /  3  = 133.3333 MHz
+ *  011:   100 *  7 /  6  = 116.6667 MHz
+ *  100:   100 *  4 /  5  =  80.0000 MHz
+ */
+static const struct freq_desc freq_desc_byt = {
+	.use_msr_plat = true,
+	.muldiv = { { 5, 6 }, { 1, 1 }, { 4, 3 }, { 7, 6 },
+		    { 4, 5 } },
+	.mask = 0x07,
+};
+
+/*
+ * Cherry Trail SDM MSR_FSB_FREQ frequencies simplified PLL model:
+ * 0000:   100 *  5 /  6  =  83.3333 MHz
+ * 0001:   100 *  1 /  1  = 100.0000 MHz
+ * 0010:   100 *  4 /  3  = 133.3333 MHz
+ * 0011:   100 *  7 /  6  = 116.6667 MHz
+ * 0100:   100 *  4 /  5  =  80.0000 MHz
+ * 0101:   100 * 14 / 15  =  93.3333 MHz
+ * 0110:   100 *  9 / 10  =  90.0000 MHz
+ * 0111:   100 *  8 /  9  =  88.8889 MHz
+ * 1000:   100 *  7 /  8  =  87.5000 MHz
+ */
+static const struct freq_desc freq_desc_cht = {
+	.use_msr_plat = true,
+	.muldiv = { { 5, 6 }, {  1,  1 }, { 4,  3 }, { 7, 6 },
+		    { 4, 5 }, { 14, 15 }, { 9, 10 }, { 8, 9 },
+		    { 7, 8 } },
+	.mask = 0x0f,
+};
+
+/*
+ * Merriefield SDM MSR_FSB_FREQ frequencies simplified PLL model:
+ * 0001:   100 *  1 /  1  = 100.0000 MHz
+ * 0010:   100 *  4 /  3  = 133.3333 MHz
+ */
+static const struct freq_desc freq_desc_tng = {
+	.use_msr_plat = true,
+	.muldiv = { { 0, 0 }, { 1, 1 }, { 4, 3 } },
+	.mask = 0x07,
+};
+
+/*
+ * Moorefield SDM MSR_FSB_FREQ frequencies simplified PLL model:
+ * 0000:   100 *  5 /  6  =  83.3333 MHz
+ * 0001:   100 *  1 /  1  = 100.0000 MHz
+ * 0010:   100 *  4 /  3  = 133.3333 MHz
+ * 0011:   100 *  1 /  1  = 100.0000 MHz
+ */
+static const struct freq_desc freq_desc_ann = {
+	.use_msr_plat = true,
+	.muldiv = { { 5, 6 }, { 1, 1 }, { 4, 3 }, { 1, 1 } },
+	.mask = 0x0f,
+};
+
+/*
+ * 24 MHz crystal? : 24 * 13 / 4 = 78 MHz
+ * Frequency step for Lightning Mountain SoC is fixed to 78 MHz,
+ * so all the frequency entries are 78000.
+ */
+static const struct freq_desc freq_desc_lgm = {
+	.use_msr_plat = true,
+	.freqs = { 78000, 78000, 78000, 78000, 78000, 78000, 78000, 78000,
+		   78000, 78000, 78000, 78000, 78000, 78000, 78000, 78000 },
+	.mask = 0x0f,
+};
+
+static const struct x86_cpu_id tsc_msr_cpu_ids[] = {
+	X86_MATCH_INTEL_FAM6_MODEL(ATOM_SALTWELL_MID,	&freq_desc_pnw),
+	X86_MATCH_INTEL_FAM6_MODEL(ATOM_SALTWELL_TABLET,&freq_desc_clv),
+	X86_MATCH_INTEL_FAM6_MODEL(ATOM_SILVERMONT,	&freq_desc_byt),
+	X86_MATCH_INTEL_FAM6_MODEL(ATOM_SILVERMONT_MID,	&freq_desc_tng),
+	X86_MATCH_INTEL_FAM6_MODEL(ATOM_AIRMONT,	&freq_desc_cht),
+	X86_MATCH_INTEL_FAM6_MODEL(ATOM_AIRMONT_MID,	&freq_desc_ann),
+	X86_MATCH_INTEL_FAM6_MODEL(ATOM_AIRMONT_NP,	&freq_desc_lgm),
+	{}
+};
+
+/*
+ * MSR-based CPU/TSC frequency discovery for certain CPUs.
+ *
+ * Set global "lapic_timer_period" to bus_clock_cycles/jiffy
+ * Return processor base frequency in KHz, or 0 on failure.
+ */
+unsigned long cpu_khz_from_msr(void)
+{
+	u32 lo, hi, ratio, freq, tscref;
+	const struct freq_desc *freq_desc;
+	const struct x86_cpu_id *id;
+	const struct muldiv *md;
+	unsigned long res;
+	int index;
+
+	id = x86_match_cpu(tsc_msr_cpu_ids);
+	if (!id)
+		return 0;
+
+	freq_desc = (struct freq_desc *)id->driver_data;
+	if (freq_desc->use_msr_plat) {
+		rdmsr(MSR_PLATFORM_INFO, lo, hi);
+		ratio = (lo >> 8) & 0xff;
+	} else {
+		rdmsr(MSR_IA32_PERF_STATUS, lo, hi);
+		ratio = (hi >> 8) & 0x1f;
+	}
+
+	/* Get FSB FREQ ID */
+	rdmsr(MSR_FSB_FREQ, lo, hi);
+	index = lo & freq_desc->mask;
+	md = &freq_desc->muldiv[index];
+
+	/*
+	 * Note this also catches cases where the index points to an unpopulated
+	 * part of muldiv, in that case the else will set freq and res to 0.
+	 */
+	if (md->divider) {
+		tscref = TSC_REFERENCE_KHZ * md->multiplier;
+		freq = DIV_ROUND_CLOSEST(tscref, md->divider);
+		/*
+		 * Multiplying by ratio before the division has better
+		 * accuracy than just calculating freq * ratio.
+		 */
+		res = DIV_ROUND_CLOSEST(tscref * ratio, md->divider);
+	} else {
+		freq = freq_desc->freqs[index];
+		res = freq * ratio;
+	}
+
+	if (freq == 0)
+		pr_err("Error MSR_FSB_FREQ index %d is unknown\n", index);
+
+#ifdef CONFIG_X86_LOCAL_APIC
+	lapic_timer_period = (freq * 1000) / HZ;
+#endif
+
+	/*
+	 * TSC frequency determined by MSR is always considered "known"
+	 * because it is reported by HW.
+	 * Another fact is that on MSR capable platforms, PIT/HPET is
+	 * generally not available so calibration won't work at all.
+	 */
+	setup_force_cpu_cap(X86_FEATURE_TSC_KNOWN_FREQ);
+
+	/*
+	 * Unfortunately there is no way for hardware to tell whether the
+	 * TSC is reliable.  We were told by silicon design team that TSC
+	 * on Atom SoCs are always "reliable". TSC is also the only
+	 * reliable clocksource on these SoCs (HPET is either not present
+	 * or not functional) so mark TSC reliable which removes the
+	 * requirement for a watchdog clocksource.
+	 */
+	setup_force_cpu_cap(X86_FEATURE_TSC_RELIABLE);
+
+	return res;
+}