Re: [PATCH v3 5/8] firmware: smccc: lfa: Add auto_activate sysfs file
From: Andre Przywara
Date: Fri Sep 18 2026 - 10:44:57 EST
Hi Nirmoy,
On 7/10/26 16:07, Nirmoy Das wrote:
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@xxxxxxx>
---
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.
Ah, nice, thanks for staying on this!
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,
I am not super excited about adding a global variable for the smccc bus device just for this, but it's not a showstopper either. Maybe just store the kobject we need?
In any case, can you please send a patch on top of v4 I just sent, maybe as a --in-reply-to to the cover letter? This would honour your contribution, and keep this patch close to the source and separate.
Cheers,
Andre
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