[PATCH v5] x86/microcode: move away from using a fake platform device

[PATCH v5] x86/microcode: move away from using a fake platform device

[Greg Kroah-Hartman]

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.

Cc: Borislav Petkov <bp@alien8.de>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: <x86@kernel.org>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
v5: - rebase against 6.16-rc4 and actually cc: the relevant maintainers
      this time, doh!
v4: - api tweaked due to parent pointer added to faux_device create
      function.
v3: - no change
v2: - new patch in a larger series

 arch/x86/kernel/cpu/microcode/core.c | 14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)

diff --git a/arch/x86/kernel/cpu/microcode/core.c b/arch/x86/kernel/cpu/microcode/core.c
index fe50eb5b7c4a..b92e09a87c69 100644
--- a/arch/x86/kernel/cpu/microcode/core.c
+++ b/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;
 
 }
-- 
2.50.0

Re: [PATCH v5] x86/microcode: move away from using a fake platform device

[Sohil Mehta]

On 7/1/2025 3:54 AM, Greg Kroah-Hartman wrote:
> 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.
> 
> Cc: Borislav Petkov <bp@alien8.de>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: Ingo Molnar <mingo@redhat.com>
> Cc: Dave Hansen <dave.hansen@linux.intel.com>
> Cc: <x86@kernel.org>
> Cc: "H. Peter Anvin" <hpa@zytor.com>
> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> ---
> v5: - rebase against 6.16-rc4 and actually cc: the relevant maintainers
>       this time, doh!
> v4: - api tweaked due to parent pointer added to faux_device create
>       function.
> v3: - no change
> v2: - new patch in a larger series
> 
>  arch/x86/kernel/cpu/microcode/core.c | 14 +++++++-------
>  1 file changed, 7 insertions(+), 7 deletions(-)
> 
> diff --git a/arch/x86/kernel/cpu/microcode/core.c b/arch/x86/kernel/cpu/microcode/core.c
> index fe50eb5b7c4a..b92e09a87c69 100644
> --- a/arch/x86/kernel/cpu/microcode/core.c
> +++ b/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;
>  

I was going to suggest including an error print here, since
microcode_init() is quite verbose otherwise. But it looks like
faux_device_create() itself would print a message in most cases if it
can't create the device. Anyway, this isn't directly related to proposed
change.

Reviewed-by: Sohil Mehta <sohil.mehta@intel.com>

>  	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;
>  
>  }

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

[tip-bot2 for Greg Kroah-Hartman]

The following commit has been merged into the x86/microcode branch of tip:

Commit-ID:     9b355cdb63b1e43434d7ac57430d3e68de58338d
Gitweb:        https://git.kernel.org/tip/9b355cdb63b1e43434d7ac57430d3e68de58338d
Author:        Greg Kroah-Hartman <gregkh@linuxfoundation.org>
AuthorDate:    Tue, 01 Jul 2025 12:54:22 +02:00
Committer:     Borislav Petkov (AMD) <bp@alien8.de>
CommitterDate: Wed, 09 Jul 2025 13:12:08 +02:00

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
---
 arch/x86/kernel/cpu/microcode/core.c | 14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)

diff --git a/arch/x86/kernel/cpu/microcode/core.c b/arch/x86/kernel/cpu/microcode/core.c
index fe50eb5..b92e09a 100644
--- a/arch/x86/kernel/cpu/microcode/core.c
+++ b/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;
 
 }