tools/power/cpupower/debug/kernel/cpufreq-test_tsc.c

   1 // SPDX-License-Identifier: GPL-2.0-only
   2 /*
   3  * test module to check whether the TSC-based delay routine continues
   4  * to work properly after cpufreq transitions. Needs ACPI to work
   5  * properly.
   6  *
   7  * Based partly on the Power Management Timer (PMTMR) code to be found
   8  * in arch/i386/kernel/timers/timer_pm.c on recent 2.6. kernels, especially
   9  * code written by John Stultz. The read_pmtmr function was copied verbatim
  10  * from that file.
  11  *
  12  * (C) 2004 Dominik Brodowski
  13  *
  14  * To use:
  15  * 1.) pass clock=tsc to the kernel on your bootloader
  16  * 2.) modprobe this module (it'll fail)
  17  * 3.) change CPU frequency
  18  * 4.) modprobe this module again
  19  * 5.) if the third value, "diff_pmtmr", changes between 2. and 4., the
  20  *     TSC-based delay routine on the Linux kernel does not correctly
  21  *     handle the cpufreq transition. Please report this to
  22  *     linux-pm@vger.kernel.org
  23  */
  24
  25 #include <linux/kernel.h>
  26 #include <linux/module.h>
  27 #include <linux/init.h>
  28 #include <linux/delay.h>
  29 #include <linux/acpi.h>
  30 #include <asm/io.h>
  31
  32 static int pm_tmr_ioport = 0;
  33
  34 /*helper function to safely read acpi pm timesource*/
  35 static u32 read_pmtmr(void)
  36 {
  37         u32 v1=0,v2=0,v3=0;
  38         /* It has been reported that because of various broken
  39          * chipsets (ICH4, PIIX4 and PIIX4E) where the ACPI PM time
  40          * source is not latched, so you must read it multiple
  41          * times to insure a safe value is read.
  42          */
  43         do {
  44                 v1 = inl(pm_tmr_ioport);
  45                 v2 = inl(pm_tmr_ioport);
  46                 v3 = inl(pm_tmr_ioport);
  47         } while ((v1 > v2 && v1 < v3) || (v2 > v3 && v2 < v1)
  48                  || (v3 > v1 && v3 < v2));
  49
  50         /* mask the output to 24 bits */
  51         return (v2 & 0xFFFFFF);
  52 }
  53
  54 static int __init cpufreq_test_tsc(void)
  55 {
  56         u32 now, then, diff;
  57         u64 now_tsc, then_tsc, diff_tsc;
  58         int i;
  59
  60         /* the following code snipped is copied from arch/x86/kernel/acpi/boot.c
  61            of Linux v2.6.25. */
  62
  63         /* detect the location of the ACPI PM Timer */
  64         if (acpi_gbl_FADT.header.revision >= FADT2_REVISION_ID) {
  65                 /* FADT rev. 2 */
  66                 if (acpi_gbl_FADT.xpm_timer_block.space_id !=
  67                     ACPI_ADR_SPACE_SYSTEM_IO)
  68                         return 0;
  69
  70                 pm_tmr_ioport = acpi_gbl_FADT.xpm_timer_block.address;
  71                 /*
  72                  * "X" fields are optional extensions to the original V1.0
  73                  * fields, so we must selectively expand V1.0 fields if the
  74                  * corresponding X field is zero.
  75                  */
  76                 if (!pm_tmr_ioport)
  77                         pm_tmr_ioport = acpi_gbl_FADT.pm_timer_block;
  78         } else {
  79                 /* FADT rev. 1 */
  80                 pm_tmr_ioport = acpi_gbl_FADT.pm_timer_block;
  81         }
  82
  83         printk(KERN_DEBUG "start--> \n");
  84         then = read_pmtmr();
  85         then_tsc = rdtsc();
  86         for (i=0;i<20;i++) {
  87                 mdelay(100);
  88                 now = read_pmtmr();
  89                 now_tsc = rdtsc();
  90                 diff = (now - then) & 0xFFFFFF;
  91                 diff_tsc = now_tsc - then_tsc;
  92                 printk(KERN_DEBUG "t1: %08u t2: %08u diff_pmtmr: %08u diff_tsc: %016llu\n", then, now, diff, diff_tsc);
  93                 then = now;
  94                 then_tsc = now_tsc;
  95         }
  96         printk(KERN_DEBUG "<-- end \n");
  97         return -ENODEV;
  98 }
  99
 100 static void __exit cpufreq_none(void)
 101 {
 102         return;
 103 }
 104
 105 module_init(cpufreq_test_tsc)
 106 module_exit(cpufreq_none)
 107
 108
 109 MODULE_AUTHOR("Dominik Brodowski");
 110 MODULE_DESCRIPTION("Verify the TSC cpufreq notifier working correctly -- needs ACPI-enabled system");
 111 MODULE_LICENSE ("GPL");