2 * A clocksource for Linux running on HyperV.
5 * Copyright (C) 2010, Novell, Inc.
6 * Author : K. Y. Srinivasan <ksrinivasan@novell.com>
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.
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
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.
23 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
25 #include <linux/version.h>
26 #include <linux/clocksource.h>
27 #include <linux/init.h>
28 #include <linux/module.h>
29 #include <linux/pci.h>
30 #include <linux/dmi.h>
31 #include <asm/hyperv.h>
32 #include <asm/mshyperv.h>
33 #include <asm/hypervisor.h>
35 #define HV_CLOCK_SHIFT 22
37 static cycle_t
read_hv_clock(struct clocksource
*arg
)
41 * Read the partition counter to get the current tick count. This count
42 * is set to 0 when the partition is created and is incremented in
43 * 100 nanosecond units.
45 rdmsrl(HV_X64_MSR_TIME_REF_COUNT
, current_tick
);
49 static struct clocksource hyperv_cs
= {
50 .name
= "hyperv_clocksource",
51 .rating
= 400, /* use this when running on Hyperv*/
52 .read
= read_hv_clock
,
53 .mask
= CLOCKSOURCE_MASK(64),
55 * The time ref counter in HyperV is in 100ns units.
56 * The definition of mult is:
57 * mult/2^shift = ns/cyc = 100
58 * mult = (100 << shift)
60 .mult
= (100 << HV_CLOCK_SHIFT
),
61 .shift
= HV_CLOCK_SHIFT
,
64 static const struct dmi_system_id __initconst
65 hv_timesource_dmi_table
[] __maybe_unused
= {
69 DMI_MATCH(DMI_SYS_VENDOR
, "Microsoft Corporation"),
70 DMI_MATCH(DMI_PRODUCT_NAME
, "Virtual Machine"),
71 DMI_MATCH(DMI_BOARD_NAME
, "Virtual Machine"),
76 MODULE_DEVICE_TABLE(dmi
, hv_timesource_dmi_table
);
78 static const struct pci_device_id __initconst
79 hv_timesource_pci_table
[] __maybe_unused
= {
80 { PCI_DEVICE(0x1414, 0x5353) }, /* VGA compatible controller */
83 MODULE_DEVICE_TABLE(pci
, hv_timesource_pci_table
);
86 static int __init
init_hv_clocksource(void)
88 if ((x86_hyper
!= &x86_hyper_ms_hyperv
) ||
89 !(ms_hyperv
.features
& HV_X64_MSR_TIME_REF_COUNT_AVAILABLE
))
92 if (!dmi_check_system(hv_timesource_dmi_table
))
95 pr_info("Registering HyperV clock source\n");
96 return clocksource_register(&hyperv_cs
);
99 module_init(init_hv_clocksource
);
100 MODULE_DESCRIPTION("HyperV based clocksource");
101 MODULE_AUTHOR("K. Y. Srinivasan <ksrinivasan@novell.com>");
102 MODULE_LICENSE("GPL");