Re: [PATCH v3 5/8] firmware: smccc: lfa: Add auto_activate sysfs file

[Nirmoy Das <nirmoyd@nvidia.com>]

On Mon, 6 Jul 2026 15:44:45 +0200, Andre Przywara wrote:

Hi Andre,

> The Arm LFA spec places control over the actual activation process in
> the hands of the non-secure host OS. An platform initiated interrupt or
> notification signals the availability of an updateable firmware image,
> but does not necessarily need to trigger it automatically.
>
> Add a sysfs control file that guards such automatic activation. If an
> administrator wants to allow automatic platform initiated updates, they
> can activate that by echoing a "1" into the auto_activate file in the
> respective sysfs directory. Any incoming notification would then result
> in the activation triggered.
>
> Signed-off-by: Andre Przywara <andre.przywara@arm.com>
> ---
>  drivers/firmware/smccc/lfa_fw.c | 34 ++++++++++++++++++++++++++++++---
>  1 file changed, 31 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/firmware/smccc/lfa_fw.c b/drivers/firmware/smccc/lfa_fw.c
> index 5b7f9b07f6c8..ce4f966db475 100644
> --- a/drivers/firmware/smccc/lfa_fw.c
> +++ b/drivers/firmware/smccc/lfa_fw.c
> @@ -89,6 +89,7 @@ enum image_attr_names {
>  	LFA_ATTR_FORCE_CPU_RENDEZVOUS,
>  	LFA_ATTR_ACTIVATE,
>  	LFA_ATTR_CANCEL,
> +	LFA_ATTR_AUTO_ACTIVATE,
>  	LFA_ATTR_NR_IMAGES
>  };
>  
> @@ -103,6 +104,7 @@ struct fw_image {
>  	bool may_reset_cpu;
>  	bool cpu_rendezvous;
>  	bool cpu_rendezvous_forced;
> +	bool auto_activate;
>  	struct kobj_attribute image_attrs[LFA_ATTR_NR_IMAGES];
>  };
>  
> @@ -550,6 +552,28 @@ static ssize_t cancel_store(struct kobject *kobj, struct kobj_attribute *attr,
>  	return count;
>  }
>  
> +static ssize_t auto_activate_store(struct kobject *kobj,
> +				   struct kobj_attribute *attr,
> +				   const char *buf, size_t count)
> +{
> +	struct fw_image *image = kobj_to_fw_image(kobj);
> +	int ret;
> +
> +	ret = kstrtobool(buf, &image->auto_activate);
> +	if (ret)
> +		return ret;
> +
> +	return count;
> +}
> +
> +static ssize_t auto_activate_show(struct kobject *kobj,
> +				  struct kobj_attribute *attr, char *buf)
> +{
> +	struct fw_image *image = kobj_to_fw_image(kobj);
> +
> +	return sysfs_emit(buf, "%d\n", image->auto_activate);
> +}
> +
>  static struct kobj_attribute image_attrs_group[LFA_ATTR_NR_IMAGES] = {
>  	[LFA_ATTR_NAME]			= __ATTR_RO(name),
>  	[LFA_ATTR_CURRENT_VERSION]	= __ATTR_RO(current_version),
> @@ -560,7 +584,8 @@ static struct kobj_attribute image_attrs_group[LFA_ATTR_NR_IMAGES] = {
>  	[LFA_ATTR_CPU_RENDEZVOUS]	= __ATTR_RO(cpu_rendezvous),
>  	[LFA_ATTR_FORCE_CPU_RENDEZVOUS]	= __ATTR_RW(force_cpu_rendezvous),
>  	[LFA_ATTR_ACTIVATE]		= __ATTR_WO(activate),
> -	[LFA_ATTR_CANCEL]		= __ATTR_WO(cancel)
> +	[LFA_ATTR_CANCEL]		= __ATTR_WO(cancel),
> +	[LFA_ATTR_AUTO_ACTIVATE]	= __ATTR_RW(auto_activate),
>  };
>  
>  static void init_image_default_attrs(void)
> @@ -631,6 +656,7 @@ static int update_fw_image_node(char *fw_uuid, int seq_id,
>  	image->kobj.kset = lfa_kset;
>  	image->image_name = image_name;
>  	image->cpu_rendezvous_forced = true;
> +	image->auto_activate = false;

Following up on our v2 discussion about the udev anchor after the
SMCCC bus rework: I got a chance to try v3 on a real machine, and
like the faux device in v2, the SMCCC bus device also works as the
udev anchor:

  ACTION=="bind|change", SUBSYSTEM=="arm_smccc", KERNEL=="arm-smccc-lfa-*", \
          RUN+="/usr/local/sbin/lfa-auto-activate"

Matching on "bind" instead of "add" worked better when I tried it,
bind fires only after probe so /sys/firmware/lfa is already
populated.

What is still missing is a notification when the image inventory
changes at runtime. I tried the KOBJ_CHANGE approach from our v2
discussion on top of v3, emitting from the SMCCC bus device after
the image tree is refreshed, and it works: the same rule re-arms
auto_activate when the event fires. What do you think about adding
such a notification? I can send a patch on top once this series has
landed, together with an example udev rule. This is what I tested:

--- a/drivers/firmware/smccc/lfa_fw.c
+++ b/drivers/firmware/smccc/lfa_fw.c
@@ -142,6 +142,7 @@
 };
 
 static struct kset *lfa_kset;
+static struct arm_smccc_device *lfa_sdev;
 static struct workqueue_struct *fw_images_update_wq;
 static struct work_struct fw_images_update_work;
 static struct attribute *image_default_attrs[LFA_ATTR_NR_IMAGES + 1];
@@ -229,6 +230,19 @@
 
 		delete_fw_image_node(image);
 	}
+
+	/*
+	 * Notify user space only after the firmware image tree has been
+	 * fully reconciled, so that consumers reading /sys/firmware/lfa/
+	 * see a settled inventory.
+	 */
+	if (lfa_sdev) {
+		int ret = kobject_uevent(&lfa_sdev->dev.kobj, KOBJ_CHANGE);
+
+		if (ret)
+			pr_warn("failed to send inventory change uevent: %d\n",
+				ret);
+	}
 }
 
 static void set_image_flags(struct fw_image *image, int seq_id,
@@ -925,6 +939,8 @@
 	}
 	INIT_WORK(&fw_images_update_work, remove_invalid_fw_images);
 
+	lfa_sdev = sdev;
+
 	init_image_default_attrs();
 	lfa_kset = kset_create_and_add("lfa", NULL, firmware_kobj);
 	if (!lfa_kset) {
@@ -966,6 +982,7 @@
 	flush_workqueue(fw_images_update_wq);
 	destroy_workqueue(fw_images_update_wq);
 	clean_fw_images_tree();
+	lfa_sdev = NULL;
 	kset_unregister(lfa_kset);
 }

>  	set_image_flags(image, seq_id, image_flags, reg_current_ver,
>  			reg_pending_ver);
>  	if (kobject_init_and_add(&image->kobj, &image_ktype, NULL,
> @@ -700,7 +726,8 @@ static int update_fw_images_tree(void)
>  
>  /*
>   * Go through all FW images in a loop and trigger activation
> - * of all activatible and pending images.
> + * of all activatible and pending images, but only if automatic
> + * activation for that image is allowed.
>   * We have to restart enumeration after every triggered activation,
>   * since the firmware images might have changed during the activation.
>   */
> @@ -719,7 +746,8 @@ static int activate_pending_image(void)
>  			continue; /* Invalid FW component */
>  
>  		update_fw_image_pending(image);
> -		if (image->activation_capable && image->activation_pending) {
> +		if (image->activation_capable && image->activation_pending &&
> +		    image->auto_activate) {
>  			found_pending = true;
>  			break;
>  		}
> -- 
> 2.43.0

Regards,
Nirmoy