diff options
| -rw-r--r-- | arch/x86/kernel/tsc_msr.c | 128 |
1 files changed, 112 insertions, 16 deletions
diff --git a/arch/x86/kernel/tsc_msr.c b/arch/x86/kernel/tsc_msr.c index bf528aae8ece..4fec6f3a1858 100644 --- a/arch/x86/kernel/tsc_msr.c +++ b/arch/x86/kernel/tsc_msr.c @@ -15,18 +15,46 @@ #include <asm/param.h> #include <asm/tsc.h> -#define MAX_NUM_FREQS 9 +#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 msr_plat does. + * field use_msr_plat does. */ struct freq_desc { - u8 msr_plat; /* 1: use MSR_PLATFORM_INFO, 0: MSR_IA32_PERF_STATUS */ + 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; }; /* @@ -35,31 +63,81 @@ struct freq_desc { * by MSR based on SDM. */ static const struct freq_desc freq_desc_pnw = { - 0, { 0, 0, 0, 0, 0, 99840, 0, 83200 } + .use_msr_plat = false, + .freqs = { 0, 0, 0, 0, 0, 99840, 0, 83200 }, + .mask = 0x07, }; static const struct freq_desc freq_desc_clv = { - 0, { 0, 133200, 0, 0, 0, 99840, 0, 83200 } + .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 = { - 1, { 83300, 100000, 133300, 116700, 80000, 0, 0, 0 } + .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 = { - 1, { 83300, 100000, 133300, 116700, 80000, 93300, 90000, 88900, 87500 } + .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 = { - 1, { 0, 100000, 133300, 0, 0, 0, 0, 0 } + .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 = { - 1, { 83300, 100000, 133300, 100000, 0, 0, 0, 0 } + .use_msr_plat = true, + .muldiv = { { 5, 6 }, { 1, 1 }, { 4, 3 }, { 1, 1 } }, + .mask = 0x0f, }; +/* 24 MHz crystal? : 24 * 13 / 4 = 78 MHz */ static const struct freq_desc freq_desc_lgm = { - 1, { 78000, 78000, 78000, 78000, 78000, 78000, 78000, 78000 } + .use_msr_plat = true, + .freqs = { 78000, 78000, 78000, 78000, 78000, 78000, 78000, 78000 }, + .mask = 0x0f, }; static const struct x86_cpu_id tsc_msr_cpu_ids[] = { @@ -81,17 +159,19 @@ static const struct x86_cpu_id tsc_msr_cpu_ids[] = { */ unsigned long cpu_khz_from_msr(void) { - u32 lo, hi, ratio, freq; + 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->msr_plat) { + if (freq_desc->use_msr_plat) { rdmsr(MSR_PLATFORM_INFO, lo, hi); ratio = (lo >> 8) & 0xff; } else { @@ -101,12 +181,28 @@ unsigned long cpu_khz_from_msr(void) /* Get FSB FREQ ID */ rdmsr(MSR_FSB_FREQ, lo, hi); + index = lo & freq_desc->mask; + md = &freq_desc->muldiv[index]; - /* Map CPU reference clock freq ID(0-7) to CPU reference clock freq(KHz) */ - freq = freq_desc->freqs[lo & 0x7]; + /* + * 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; + } - /* TSC frequency = maximum resolved freq * maximum resolved bus ratio */ - 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; |