diff options
| -rw-r--r-- | arch/x86/kernel/tsc_msr.c | 97 |
1 files changed, 86 insertions, 11 deletions
diff --git a/arch/x86/kernel/tsc_msr.c b/arch/x86/kernel/tsc_msr.c index 95030895fffa..c65adaf81384 100644 --- a/arch/x86/kernel/tsc_msr.c +++ b/arch/x86/kernel/tsc_msr.c @@ -18,6 +18,28 @@ #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, @@ -26,6 +48,11 @@ */ 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; }; @@ -47,31 +74,66 @@ static const struct freq_desc freq_desc_clv = { .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, - .freqs = { 83300, 100000, 133300, 116700, 80000, 0, 0, 0 }, + .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, - .freqs = { 83300, 100000, 133300, 116700, 80000, 93300, 90000, - 88900, 87500 }, + .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, - .freqs = { 0, 100000, 133300, 0, 0, 0, 0, 0 }, + .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, - .freqs = { 83300, 100000, 133300, 100000, 0, 0, 0, 0 }, + .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 = { .use_msr_plat = true, .freqs = { 78000, 78000, 78000, 78000, 78000, 78000, 78000, 78000 }, @@ -97,9 +159,10 @@ 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; @@ -119,12 +182,24 @@ 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[index]; - - /* TSC frequency = maximum resolved freq * maximum resolved bus ratio */ - res = freq * ratio; + /* + * 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); |