[RFC PATCH 2/2] platform/x86: Add virtual PMC driver used for S2Idle

[Grzegorz Jaszczyk <jaz@semihalf.com>]

Virtual PMC driver is meant for the guest VMs for the S2Idle
notification. Its purpose is to register S2Idle dev ops notify handler,
which will evaluate ACPI _DSM as a very last command before the guest
enters S2Idle power state.

This allows to trap on MMIO access done as a consequence of _DSM
evaluation and therefore notify the VMM about the guest entering S2Idle
state.

Signed-off-by: Grzegorz Jaszczyk <jaz@semihalf.com>
---
 drivers/platform/x86/Kconfig    |  7 ++++
 drivers/platform/x86/Makefile   |  1 +
 drivers/platform/x86/virt_pmc.c | 73 +++++++++++++++++++++++++++++++++
 3 files changed, 81 insertions(+)
 create mode 100644 drivers/platform/x86/virt_pmc.c

diff --git a/drivers/platform/x86/Kconfig b/drivers/platform/x86/Kconfig
index bc4013e950ed..dee974321b01 100644
--- a/drivers/platform/x86/Kconfig
+++ b/drivers/platform/x86/Kconfig
@@ -479,6 +479,13 @@ config WIRELESS_HOTKEY
 	 To compile this driver as a module, choose M here: the module will
 	 be called wireless-hotkey.
 
+config VIRT_PMC
+	tristate "Virt PMC"
+	depends on ACPI && SUSPEND
+	help
+	  The Virtual PMC driver is meant for the guest VMs and it's main
+	  purpose is to notify about guest entering s2idle state.
+
 config HP_WMI
 	tristate "HP WMI extras"
 	depends on ACPI_WMI
diff --git a/drivers/platform/x86/Makefile b/drivers/platform/x86/Makefile
index 4a59f47a46e2..3c3e440f11bb 100644
--- a/drivers/platform/x86/Makefile
+++ b/drivers/platform/x86/Makefile
@@ -116,6 +116,7 @@ obj-$(CONFIG_MLX_PLATFORM)		+= mlx-platform.o
 obj-$(CONFIG_TOUCHSCREEN_DMI)		+= touchscreen_dmi.o
 obj-$(CONFIG_WIRELESS_HOTKEY)		+= wireless-hotkey.o
 obj-$(CONFIG_X86_ANDROID_TABLETS)	+= x86-android-tablets.o
+obj-$(CONFIG_VIRT_PMC)			+= virt_pmc.o
 
 # Intel uncore drivers
 obj-$(CONFIG_INTEL_IPS)				+= intel_ips.o
diff --git a/drivers/platform/x86/virt_pmc.c b/drivers/platform/x86/virt_pmc.c
new file mode 100644
index 000000000000..d0607db6cd22
--- /dev/null
+++ b/drivers/platform/x86/virt_pmc.c
@@ -0,0 +1,73 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Virtual Power Management Controller Driver
+ *
+ * Author: Grzegorz Jaszczyk <jaz@semihalf.com>
+ */
+
+#include <linux/acpi.h>
+#include <linux/platform_device.h>
+
+#define ACPI_VIRT_PMC_DSM_UUID	"9ea49ba3-434a-49a6-be30-37cc55c4d397"
+#define ACPI_VIRT_PMC_NOTIFY 1
+
+static acpi_handle virt_pmc_handle;
+
+static void virt_pmc_s2idle_notify(void)
+{
+	union acpi_object *out_obj;
+	static guid_t dsm_guid;
+
+	guid_parse(ACPI_VIRT_PMC_DSM_UUID, &dsm_guid);
+
+	out_obj = acpi_evaluate_dsm(virt_pmc_handle, &dsm_guid,
+					0, ACPI_VIRT_PMC_NOTIFY, NULL);
+
+	acpi_handle_debug(virt_pmc_handle, "_DSM function %u evaluation %s\n",
+			  ACPI_VIRT_PMC_NOTIFY, out_obj ? "successful" : "failed");
+
+	ACPI_FREE(out_obj);
+}
+
+static struct acpi_s2idle_dev_ops amd_pmc_s2idle_dev_ops = {
+	.notify = virt_pmc_s2idle_notify,
+};
+
+static int virt_pmc_probe(struct platform_device *pdev)
+{
+	int err = 0;
+
+	virt_pmc_handle = ACPI_HANDLE(&pdev->dev);
+
+	err = acpi_register_lps0_dev(&amd_pmc_s2idle_dev_ops);
+	if (err)
+		dev_warn(&pdev->dev, "failed to register LPS0 sleep handler\n");
+
+	return err;
+}
+
+static int virt_pmc_remove(struct platform_device *pdev)
+{
+	acpi_unregister_lps0_dev(&amd_pmc_s2idle_dev_ops);
+
+	return 0;
+}
+
+static const struct acpi_device_id virt_pmc_acpi_ids[] = {
+	{"HYPE0001", 0}, /* _HID for XXX Power Engine, _CID PNP0D80*/
+	{ }
+};
+MODULE_DEVICE_TABLE(acpi, virt_pmc_acpi_ids);
+
+static struct platform_driver virt_pmc_driver = {
+	.driver = {
+		.name = "virtual_pmc",
+		.acpi_match_table = ACPI_PTR(virt_pmc_acpi_ids),
+	},
+	.probe = virt_pmc_probe,
+	.remove = virt_pmc_remove,
+};
+
+module_platform_driver(virt_pmc_driver);
+
+MODULE_DESCRIPTION("Virtual PMC Driver");
-- 
2.37.0.rc0.161.g10f37bed90-goog