x86/kernel/tsc_msr.c

1 // SPDX-License-Identifier: GPL-2.0
14 #include <asm/intel-family.h>
63  * so the freq number is not exactly the same as reported
161  * MSR-based CPU/TSC frequency discovery for certain CPUs.
164  * Return processor base frequency in KHz, or 0 on failure.
168 	u32 lo, hi, ratio, freq, tscref;  in cpu_khz_from_msr()  local
179 	freq_desc = (struct freq_desc *)id->driver_data;  in cpu_khz_from_msr()
180 	if (freq_desc->use_msr_plat) {  in cpu_khz_from_msr()
181 		rdmsr(MSR_PLATFORM_INFO, lo, hi);  in cpu_khz_from_msr()
182 		ratio = (lo >> 8) & 0xff;  in cpu_khz_from_msr()
184 		rdmsr(MSR_IA32_PERF_STATUS, lo, hi);  in cpu_khz_from_msr()
188 	/* Get FSB FREQ ID */  in cpu_khz_from_msr()
189 	rdmsr(MSR_FSB_FREQ, lo, hi);  in cpu_khz_from_msr()
190 	index = lo & freq_desc->mask;  in cpu_khz_from_msr()
191 	md = &freq_desc->muldiv[index];  in cpu_khz_from_msr()
195 	 * part of muldiv, in that case the else will set freq and res to 0.  in cpu_khz_from_msr()
197 	if (md->divider) {  in cpu_khz_from_msr()
198 		tscref = TSC_REFERENCE_KHZ * md->multiplier;  in cpu_khz_from_msr()
199 		freq = DIV_ROUND_CLOSEST(tscref, md->divider);  in cpu_khz_from_msr()
202 		 * accuracy than just calculating freq * ratio.  in cpu_khz_from_msr()
204 		res = DIV_ROUND_CLOSEST(tscref * ratio, md->divider);  in cpu_khz_from_msr()
206 		freq = freq_desc->freqs[index];  in cpu_khz_from_msr()
207 		res = freq * ratio;  in cpu_khz_from_msr()
210 	if (freq == 0)  in cpu_khz_from_msr()
214 	lapic_timer_period = (freq * 1000) / HZ;  in cpu_khz_from_msr()