drivers/staging/hv/hv_timesource.c

   1 /*
   2  * A clocksource for Linux running on HyperV.
   3  *
   4  *
   5  * Copyright (C) 2010, Novell, Inc.
   6  * Author : K. Y. Srinivasan <ksrinivasan@novell.com>
   7  *
   8  * This program is free software; you can redistribute it and/or modify
   9  * it under the terms of the GNU General Public License version 2 as
  10  * published by the Free Software Foundation.
  11  *
  12  * This program is distributed in the hope that it will be useful, but
  13  * WITHOUT ANY WARRANTY; without even the implied warranty of
  14  * MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE, GOOD TITLE or
  15  * NON INFRINGEMENT.  See the GNU General Public License for more
  16  * details.
  17  *
  18  * You should have received a copy of the GNU General Public License
  19  * along with this program; if not, write to the Free Software
  20  * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  21  *
  22  */
  23 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
  24
  25 #include <linux/clocksource.h>
  26 #include <linux/init.h>
  27 #include <linux/module.h>
  28 #include <linux/pci.h>
  29 #include <linux/dmi.h>
  30 #include <asm/hyperv.h>
  31 #include <asm/mshyperv.h>
  32 #include <asm/hypervisor.h>
  33
  34 #define HV_CLOCK_SHIFT  22
  35
  36 static cycle_t read_hv_clock(struct clocksource *arg)
  37 {
  38         cycle_t current_tick;
  39         /*
  40          * Read the partition counter to get the current tick count. This count
  41          * is set to 0 when the partition is created and is incremented in
  42          * 100 nanosecond units.
  43          */
  44         rdmsrl(HV_X64_MSR_TIME_REF_COUNT, current_tick);
  45         return current_tick;
  46 }
  47
  48 static struct clocksource hyperv_cs = {
  49         .name           = "hyperv_clocksource",
  50         .rating         = 400, /* use this when running on Hyperv*/
  51         .read           = read_hv_clock,
  52         .mask           = CLOCKSOURCE_MASK(64),
  53         /*
  54          * The time ref counter in HyperV is in 100ns units.
  55          * The definition of mult is:
  56          * mult/2^shift = ns/cyc = 100
  57          * mult = (100 << shift)
  58          */
  59         .mult           = (100 << HV_CLOCK_SHIFT),
  60         .shift          = HV_CLOCK_SHIFT,
  61 };
  62
  63 static const struct dmi_system_id __initconst
  64 hv_timesource_dmi_table[] __maybe_unused  = {
  65         {
  66                 .ident = "Hyper-V",
  67                 .matches = {
  68                         DMI_MATCH(DMI_SYS_VENDOR, "Microsoft Corporation"),
  69                         DMI_MATCH(DMI_PRODUCT_NAME, "Virtual Machine"),
  70                         DMI_MATCH(DMI_BOARD_NAME, "Virtual Machine"),
  71                 },
  72         },
  73         { },
  74 };
  75 MODULE_DEVICE_TABLE(dmi, hv_timesource_dmi_table);
  76
  77 static const struct pci_device_id __initconst
  78 hv_timesource_pci_table[] __maybe_unused = {
  79         { PCI_DEVICE(0x1414, 0x5353) }, /* VGA compatible controller */
  80         { 0 }
  81 };
  82 MODULE_DEVICE_TABLE(pci, hv_timesource_pci_table);
  83
  84
  85 static int __init init_hv_clocksource(void)
  86 {
  87         if ((x86_hyper != &x86_hyper_ms_hyperv) ||
  88                 !(ms_hyperv.features & HV_X64_MSR_TIME_REF_COUNT_AVAILABLE))
  89                 return -ENODEV;
  90
  91         if (!dmi_check_system(hv_timesource_dmi_table))
  92                 return -ENODEV;
  93
  94         pr_info("Registering HyperV clock source\n");
  95         return clocksource_register(&hyperv_cs);
  96 }
  97
  98 module_init(init_hv_clocksource);
  99 MODULE_DESCRIPTION("HyperV based clocksource");
 100 MODULE_AUTHOR("K. Y. Srinivasan <ksrinivasan@novell.com>");
 101 MODULE_LICENSE("GPL");