[PATCH 1/2] uacce: add device usage sysfs interface

[Weili Qian]

Userspace has no way to query the runtime usage of a UACCE
device; it can only be inferred indirectly from queue state, which is
neither accurate nor uniform across drivers.

Add a read-only dev_usage sysfs attribute and a get_dev_usage callback
in struct uacce_ops. A driver implementing the callback writes the
current usage as a percentage (0-100) string into the caller-provided
buffer and returns the number of bytes written; dev_usage_show()
appends the trailing newline. The attribute is hidden via
uacce_dev_is_visible() when the driver does not provide the callback.

The corresponding ABI entry is added to Documentation/ABI/testing/
sysfs-driver-uacce.

Signed-off-by: Weili Qian <qianweili@xxxxxxxxxx>
---
 Documentation/ABI/testing/sysfs-driver-uacce |  9 +++++++++
 drivers/misc/uacce/uacce.c                   | 19 +++++++++++++++++++
 include/linux/uacce.h                        |  5 +++++
 3 files changed, 33 insertions(+)

diff --git a/Documentation/ABI/testing/sysfs-driver-uacce b/Documentation/ABI/testing/sysfs-driver-uacce
index d3f0b8f3c589..3e4af4c1e5a9 100644
--- a/Documentation/ABI/testing/sysfs-driver-uacce
+++ b/Documentation/ABI/testing/sysfs-driver-uacce
@@ -55,3 +55,12 @@ Date:           Feb 2020
 KernelVersion:  5.7
 Contact:        linux-accelerators@xxxxxxxxxxxxxxxx
 Description:    Size (bytes) of dus region queue file
+
+What:           /sys/class/uacce/<dev_name>/dev_usage
+Date:           Sep 2026
+KernelVersion:  7.3
+Contact:        linux-accelerators@xxxxxxxxxxxxxxxx
+Description:    (R) Current usage of the device, reported as a driver-defined
+                string of up to PAGE_SIZE - 1 bytes. Usage is expressed as a
+                percentage (0-100). The attribute is hidden if the driver does
+                not implement the get_dev_usage callback.
diff --git a/drivers/misc/uacce/uacce.c b/drivers/misc/uacce/uacce.c
index 45521d4a56d1..545ba35a590b 100644
--- a/drivers/misc/uacce/uacce.c
+++ b/drivers/misc/uacce/uacce.c
@@ -433,6 +433,20 @@ static ssize_t isolate_strategy_store(struct device *dev, struct device_attribut
 	return count;
 }
 
+static ssize_t dev_usage_show(struct device *dev, struct device_attribute *attr, char *buf)
+{
+	struct uacce_device *uacce = to_uacce_device(dev);
+	int ret;
+
+	ret = uacce->ops->get_dev_usage(uacce, buf, PAGE_SIZE - 1);
+	if (ret < 0)
+		return ret;
+
+	buf[ret++] = '\n';
+
+	return ret;
+}
+
 static DEVICE_ATTR_RO(api);
 static DEVICE_ATTR_RO(flags);
 static DEVICE_ATTR_RO(available_instances);
@@ -441,6 +455,7 @@ static DEVICE_ATTR_RO(region_mmio_size);
 static DEVICE_ATTR_RO(region_dus_size);
 static DEVICE_ATTR_RO(isolate);
 static DEVICE_ATTR_RW(isolate_strategy);
+static DEVICE_ATTR_RO(dev_usage);
 
 static struct attribute *uacce_dev_attrs[] = {
 	&dev_attr_api.attr,
@@ -451,6 +466,7 @@ static struct attribute *uacce_dev_attrs[] = {
 	&dev_attr_region_dus_size.attr,
 	&dev_attr_isolate.attr,
 	&dev_attr_isolate_strategy.attr,
+	&dev_attr_dev_usage.attr,
 	NULL,
 };
 
@@ -474,6 +490,9 @@ static umode_t uacce_dev_is_visible(struct kobject *kobj,
 	if (attr == &dev_attr_isolate.attr && !uacce->ops->get_isolate_state)
 		return 0;
 
+	if (attr == &dev_attr_dev_usage.attr && !uacce->ops->get_dev_usage)
+		return 0;
+
 	return attr->mode;
 }
 
diff --git a/include/linux/uacce.h b/include/linux/uacce.h
index e290c0269944..8f0b9765e4b6 100644
--- a/include/linux/uacce.h
+++ b/include/linux/uacce.h
@@ -34,6 +34,10 @@ struct uacce_qfile_region {
  * @get_isolate_state: get the device state after set the isolate strategy
  * @isolate_err_threshold_write: stored the isolate error threshold to the device
  * @isolate_err_threshold_read: read the isolate error threshold value from the device
+ * @get_dev_usage: get the device usage. Write a string describing current
+ *                 usage as a percentage (0-100) into @buf, at most @size
+ *                 bytes, without a trailing newline. Return the number of
+ *                 bytes written on success or a negative errno on failure.
  */
 struct uacce_ops {
 	int (*get_available_instances)(struct uacce_device *uacce);
@@ -50,6 +54,7 @@ struct uacce_ops {
 	enum uacce_dev_state (*get_isolate_state)(struct uacce_device *uacce);
 	int (*isolate_err_threshold_write)(struct uacce_device *uacce, u32 num);
 	u32 (*isolate_err_threshold_read)(struct uacce_device *uacce);
+	int (*get_dev_usage)(struct uacce_device *uacce, char *buf, int size);
 };
 
 /**
-- 
2.43.0