BACKPORT: FROMLIST: virt: gunyah: Add hypervisor driver

Add driver to detect when running under Gunyah. It performs basic
identification hypercall and populates the platform bus for resource
manager to probe.

Bug: 338347082
Link: https://lore.kernel.org/all/20240222-gunyah-v17-5-1e9da6763d38@quicinc.com/
Change-Id: Ie18fa6bf01f0d9b66c0e657abf8581d9ef186056
Signed-off-by: Elliot Berman <quic_eberman@quicinc.com>
Signed-off-by: Sreenad Menon <quic_sreemeno@quicinc.com>
[Elliot: resolve trivial conflicts in drivers/virt/Makefile]
Signed-off-by: Elliot Berman <elliot.berman@oss.qualcomm.com>

drivers/virt/Makefile

@@ -10,3 +10,4 @@ obj-y				+= vboxguest/
 obj-$(CONFIG_NITRO_ENCLAVES)	+= nitro_enclaves/
 obj-$(CONFIG_ACRN_HSM)		+= acrn/
 obj-y				+= coco/
+obj-y				+= gunyah/

drivers/virt/gunyah/Makefile

@@ -0,0 +1,3 @@
+# SPDX-License-Identifier: GPL-2.0
+
+obj-$(CONFIG_GUNYAH) += gunyah.o

drivers/virt/gunyah/gunyah.c

@@ -0,0 +1,52 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (c) 2023-2024 Qualcomm Innovation Center, Inc. All rights reserved.
+ */
+
+#include <linux/gunyah.h>
+#include <linux/module.h>
+#include <linux/of_platform.h>
+#include <linux/platform_device.h>
+
+static int gunyah_probe(struct platform_device *pdev)
+{
+	struct gunyah_hypercall_hyp_identify_resp gunyah_api;
+
+	if (!arch_is_gunyah_guest())
+		return -ENODEV;
+
+	gunyah_hypercall_hyp_identify(&gunyah_api);
+
+	pr_info("Running under Gunyah hypervisor %llx/v%u\n",
+		FIELD_GET(GUNYAH_API_INFO_VARIANT_MASK, gunyah_api.api_info),
+		gunyah_api_version(&gunyah_api));
+
+	/* Might move this out to individual drivers if there's ever an API version bump */
+	if (gunyah_api_version(&gunyah_api) != GUNYAH_API_V1) {
+		pr_info("Unsupported Gunyah version: %u\n",
+			gunyah_api_version(&gunyah_api));
+		return -ENODEV;
+	}
+
+	return devm_of_platform_populate(&pdev->dev);
+}
+
+static const struct of_device_id gunyah_of_match[] = {
+	{ .compatible = "gunyah-hypervisor" },
+	{}
+};
+MODULE_DEVICE_TABLE(of, gunyah_of_match);
+
+/* clang-format off */
+static struct platform_driver gunyah_driver = {
+	.probe = gunyah_probe,
+	.driver = {
+		.name = "gunyah",
+		.of_match_table = gunyah_of_match,
+	}
+};
+/* clang-format on */
+module_platform_driver(gunyah_driver);
+
+MODULE_LICENSE("GPL");
+MODULE_DESCRIPTION("Gunyah Driver");