x86/microcode: Move away from using a fake platform device

Downloading firmware needs a device to hang off of, and so a platform device
seemed like the simplest way to do this.  Now that we have a faux device
interface, use that instead as this "microcode device" is not anything
resembling a platform device at all.

Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Reviewed-by: Sohil Mehta <sohil.mehta@intel.com>
Link: https://lore.kernel.org/2025070121-omission-small-9308@gregkh

Author: gregkh

arch/x86/kernel/cpu/microcode/core.c

@@ -17,8 +17,8 @@
 
 #define pr_fmt(fmt) "microcode: " fmt
 
-#include <linux/platform_device.h>
 #include <linux/stop_machine.h>
+#include <linux/device/faux.h>
 #include <linux/syscore_ops.h>
 #include <linux/miscdevice.h>
 #include <linux/capability.h>
@@ -249,7 +249,7 @@ static void reload_early_microcode(unsigned int cpu)
 }
 
 /* fake device for request_firmware */
-static struct platform_device	*microcode_pdev;
+static struct faux_device *microcode_fdev;
 
 #ifdef CONFIG_MICROCODE_LATE_LOADING
 /*
@@ -690,7 +690,7 @@ static int load_late_locked(void)
 	if (!setup_cpus())
 		return -EBUSY;
 
-	switch (microcode_ops->request_microcode_fw(0, &microcode_pdev->dev)) {
+	switch (microcode_ops->request_microcode_fw(0, &microcode_fdev->dev)) {
 	case UCODE_NEW:
 		return load_late_stop_cpus(false);
 	case UCODE_NEW_SAFE:
@@ -841,9 +841,9 @@ static int __init microcode_init(void)
 	if (early_data.new_rev)
 		pr_info_once("Updated early from: 0x%08x\n", early_data.old_rev);
 
-	microcode_pdev = platform_device_register_simple("microcode", -1, NULL, 0);
-	if (IS_ERR(microcode_pdev))
-		return PTR_ERR(microcode_pdev);
+	microcode_fdev = faux_device_create("microcode", NULL, NULL);
+	if (!microcode_fdev)
+		return -ENODEV;
 
 	dev_root = bus_get_dev_root(&cpu_subsys);
 	if (dev_root) {
@@ -862,7 +862,7 @@ static int __init microcode_init(void)
 	return 0;
 
  out_pdev:
-	platform_device_unregister(microcode_pdev);
+	faux_device_destroy(microcode_fdev);
 	return error;
 
 }