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

[Greg KH]

On Mon, Sep 21, 2026 at 03:51:30PM +0800, Weili Qian wrote:
> 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

That's not going to happen here :(

> +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);

Why can't you use sysfs_emit()?  That way you don't have to worry about
PAGE_SIZE, and you don't have to do:

> +	if (ret < 0)
> +		return ret;
> +
> +	buf[ret++] = '\n';

That type of thing :(

Also, you got your math wrong above :(

> +
> +	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.

Why the newline thing?

thanks,

greg k-h