Re: A clocksource driver for HyperV

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On 04/05/2010 01:30 PM, Ky Srinivasan wrote:
+static cycle_t read_hv_clock(struct clocksource *arg)
+{
+	cycle_t current_tick;
+	/*
+	 * Read the partition counter to get the current tick count. This count
+	 * is set to 0 when the partition is created and is incremented in
+	 * 100 nanosecond units.
+	 */
+	rdmsrl(HV_X64_MSR_TIME_REF_COUNT, current_tick);
+	return current_tick;
+}
+
+static struct clocksource clocksource_hyperv = {
+	.name           = "hyperv_clocksource",

Seems like a redundantly long name; any use of this string is going to be in a context where it is obviously a clocksource. How about just "hyperv"?

+	.rating         = 400, /* use this when running on Hyperv*/
+	.read           = read_hv_clock,
+	.mask           = CLOCKSOURCE_MASK(64),
+	.shift          = HV_CLOCK_SHIFT,
+};
+
+static struct dmi_system_id __initconst
+hv_timesource_dmi_table[] __maybe_unused  = {
+	{
+		.ident = "Hyper-V",
+		.matches = {
+			DMI_MATCH(DMI_SYS_VENDOR, "Microsoft Corporation"),
+			DMI_MATCH(DMI_PRODUCT_NAME, "Virtual Machine"),
+			DMI_MATCH(DMI_BOARD_NAME, "Virtual Machine"),
+		},
+	},
+	{ },
+};
+MODULE_DEVICE_TABLE(dmi, hv_timesource_dmi_table);

So you use the DMI signatures to determine whether the module is needed, but cpuid to work out if the feature is present?

+
+static struct pci_device_id __initconst
+hv_timesource_pci_table[] __maybe_unused = {
+	{ PCI_DEVICE(0x1414, 0x5353) }, /* VGA compatible controller */
+	{ 0 }
+};
+MODULE_DEVICE_TABLE(pci, hv_timesource_pci_table);

And/or PCI?

Seems a bit... ad-hoc? Is this the official way to determine the presence of Hyper-V?

+
+
+static int __init hv_detect_hyperv(void)

This looks generally useful. Should it be hidden away in the clocksource driver, or in some common hyper-v code? Do other hyper-v drivers have versions of this?

+{
+	u32 eax, ebx, ecx, edx;
+	static char hyp_signature[20];
20?  static?

+
+	cpuid(1,&eax,&ebx,&ecx,&edx);
+	if (!(ecx&  HV_HYPERVISOR_PRESENT_BIT)) {
+		printk(KERN_WARNING
+			"Not on a Hypervisor\n");
This just looks like noise, especially since it doesn't identify what is generating the message. And if you compile this code in as =y (non-modular) then it will complain every boot.

+		return 1;
+	}
+	cpuid(HV_CPUID_SIGNATURE,&eax,&ebx,&ecx,&edx);
+	*(u32 *)(hyp_signature + 0) = ebx;
+	*(u32 *)(hyp_signature + 4) = ecx;
+	*(u32 *)(hyp_signature + 8) = edx;
+	hyp_signature[12] = 0;
+
+	if ((eax<  HV_CPUID_MIN) || (strcmp("Microsoft Hv", hyp_signature))) {

memcmp, surely?

+		printk(KERN_WARNING
+			"Not on HyperV; signature %s, eax %x\n",
+			hyp_signature, eax);
+		return 1;
+	}
+	/*
+	 * Extract the features, recommendations etc.
+	 */
+	cpuid(HV_CPUID_FEATURES,&eax,&ebx,&ecx,&edx);
+	if (!(eax&  0x10)) {
+		printk(KERN_WARNING "HyperV Time Ref Counter not available!\n");
+		return 1;
+	}
+
+	cpuid(HV_CPUID_RECOMMENDATIONS,&eax,&ebx,&ecx,&edx);
+	printk(KERN_INFO "HyperV recommendations: %x\n", eax);
+	printk(KERN_INFO "HyperV spin count: %x\n", ebx);
+	return 0;
+}
+
+
+static int __init init_hv_clocksource(void)
+{
+	if (hv_detect_hyperv())
+		return -ENODEV;
+	/*
+	 * The time ref counter in HyperV is in 100ns units.
+	 * The definition of mult is:
+	 * mult/2^shift = ns/cyc = 100
+	 * mult = (100<<  shift)
+	 */
+	clocksource_hyperv.mult = (100<<  HV_CLOCK_SHIFT);

Why not initialize this in the structure?  It's just 100<<22 isn't it?

+	printk(KERN_INFO "Registering HyperV clock source\n");
+	return clocksource_register(&clocksource_hyperv);
+}
+
+module_init(init_hv_clocksource);
+MODULE_DESCRIPTION("HyperV based clocksource");
+MODULE_AUTHOR("K. Y. Srinivasan<ksrinivasan@xxxxxxxxxx>");
+MODULE_LICENSE("GPL");
Index: linux/drivers/staging/hv/Makefile
===================================================================
--- linux.orig/drivers/staging/hv/Makefile	2010-04-05 13:02:06.000000000 -0600
+++ linux/drivers/staging/hv/Makefile	2010-04-05 13:02:13.000000000 -0600
@@ -1,4 +1,4 @@
-obj-$(CONFIG_HYPERV)		+= hv_vmbus.o
+obj-$(CONFIG_HYPERV)		+= hv_vmbus.o hv_timesource.o
  obj-$(CONFIG_HYPERV_STORAGE)	+= hv_storvsc.o
  obj-$(CONFIG_HYPERV_BLOCK)	+= hv_blkvsc.o
  obj-$(CONFIG_HYPERV_NET)	+= hv_netvsc.o

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