1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
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;
}
|
