Re: [PATCH v7 2/4] drm/panthor: Add driver IOCTL for setting BO labels

[Steven Price <steven.price@arm.com>]

On 11/04/2025 16:03, Adrián Larumbe wrote:
> Allow UM to label a BO for which it possesses a DRM handle.
> 
> Signed-off-by: Adrián Larumbe <adrian.larumbe@collabora.com>
> Reviewed-by: Liviu Dudau <liviu.dudau@arm.com>
> Reviewed-by: Boris Brezillon <boris.brezillon@collabora.com>

Reviewed-by: Steven Price <steven.price@arm.com>

Although very minor NITs below which you can consider.

> ---
>  drivers/gpu/drm/panthor/panthor_drv.c | 42 ++++++++++++++++++++++++++-
>  drivers/gpu/drm/panthor/panthor_gem.h |  2 ++
>  include/uapi/drm/panthor_drm.h        | 23 +++++++++++++++
>  3 files changed, 66 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/panthor/panthor_drv.c b/drivers/gpu/drm/panthor/panthor_drv.c
> index 06fe46e32073..983b24f1236c 100644
> --- a/drivers/gpu/drm/panthor/panthor_drv.c
> +++ b/drivers/gpu/drm/panthor/panthor_drv.c
> @@ -1331,6 +1331,44 @@ static int panthor_ioctl_vm_get_state(struct drm_device *ddev, void *data,
>  	return 0;
>  }
>  
> +static int panthor_ioctl_bo_set_label(struct drm_device *ddev, void *data,
> +				  struct drm_file *file)
> +{
> +	struct drm_panthor_bo_set_label *args = data;
> +	struct drm_gem_object *obj;
> +	const char *label;
> +	int ret = 0;
> +
> +	obj = drm_gem_object_lookup(file, args->handle);
> +	if (!obj)
> +		return -ENOENT;
> +
> +	if (args->size && args->label) {
> +		if (args->size > PANTHOR_BO_LABEL_MAXLEN) {
> +			ret = -E2BIG;
> +			goto err_label;
> +		}
> +
> +		label = strndup_user(u64_to_user_ptr(args->label), args->size);
> +		if (IS_ERR(label)) {
> +			ret = PTR_ERR(label);
> +			goto err_label;
> +		}
> +	} else if (args->size && !args->label) {
> +		ret = -EINVAL;
> +		goto err_label;
> +	} else {
> +		label = NULL;
> +	}
> +
> +	panthor_gem_bo_set_label(obj, label);
> +
> +err_label:
> +	drm_gem_object_put(obj);
> +
> +	return ret;
> +}
> +
>  static int
>  panthor_open(struct drm_device *ddev, struct drm_file *file)
>  {
> @@ -1400,6 +1438,7 @@ static const struct drm_ioctl_desc panthor_drm_driver_ioctls[] = {
>  	PANTHOR_IOCTL(TILER_HEAP_CREATE, tiler_heap_create, DRM_RENDER_ALLOW),
>  	PANTHOR_IOCTL(TILER_HEAP_DESTROY, tiler_heap_destroy, DRM_RENDER_ALLOW),
>  	PANTHOR_IOCTL(GROUP_SUBMIT, group_submit, DRM_RENDER_ALLOW),
> +	PANTHOR_IOCTL(BO_SET_LABEL, bo_set_label, DRM_RENDER_ALLOW),
>  };
>  
>  static int panthor_mmap(struct file *filp, struct vm_area_struct *vma)
> @@ -1509,6 +1548,7 @@ static void panthor_debugfs_init(struct drm_minor *minor)
>   * - 1.2 - adds DEV_QUERY_GROUP_PRIORITIES_INFO query
>   *       - adds PANTHOR_GROUP_PRIORITY_REALTIME priority
>   * - 1.3 - adds DRM_PANTHOR_GROUP_STATE_INNOCENT flag
> + * - 1.4 - adds DRM_IOCTL_PANTHOR_BO_SET_LABEL ioctl
>   */
>  static const struct drm_driver panthor_drm_driver = {
>  	.driver_features = DRIVER_RENDER | DRIVER_GEM | DRIVER_SYNCOBJ |
> @@ -1522,7 +1562,7 @@ static const struct drm_driver panthor_drm_driver = {
>  	.name = "panthor",
>  	.desc = "Panthor DRM driver",
>  	.major = 1,
> -	.minor = 3,
> +	.minor = 4,
>  
>  	.gem_create_object = panthor_gem_create_object,
>  	.gem_prime_import_sg_table = drm_gem_shmem_prime_import_sg_table,
> diff --git a/drivers/gpu/drm/panthor/panthor_gem.h b/drivers/gpu/drm/panthor/panthor_gem.h
> index af0d77338860..beba066b4974 100644
> --- a/drivers/gpu/drm/panthor/panthor_gem.h
> +++ b/drivers/gpu/drm/panthor/panthor_gem.h
> @@ -13,6 +13,8 @@
>  
>  struct panthor_vm;
>  
> +#define PANTHOR_BO_LABEL_MAXLEN	PAGE_SIZE
> +
>  /**
>   * struct panthor_gem_object - Driver specific GEM object.
>   */
> diff --git a/include/uapi/drm/panthor_drm.h b/include/uapi/drm/panthor_drm.h
> index 97e2c4510e69..12b1994499a9 100644
> --- a/include/uapi/drm/panthor_drm.h
> +++ b/include/uapi/drm/panthor_drm.h
> @@ -127,6 +127,9 @@ enum drm_panthor_ioctl_id {
>  
>  	/** @DRM_PANTHOR_TILER_HEAP_DESTROY: Destroy a tiler heap. */
>  	DRM_PANTHOR_TILER_HEAP_DESTROY,
> +
> +	/** @DRM_PANTHOR_BO_SET_LABEL: Label a BO. */
> +	DRM_PANTHOR_BO_SET_LABEL,
>  };
>  
>  /**
> @@ -977,6 +980,24 @@ struct drm_panthor_tiler_heap_destroy {
>  	__u32 pad;
>  };
>  
> +/**
> + * struct drm_panthor_bo_set_label - Arguments passed to DRM_IOCTL_PANTHOR_BO_SET_LABEL
> + */
> +struct drm_panthor_bo_set_label {
> +	/** @handle: Handle of the buffer object to label. */
> +	__u32 handle;
> +
> +	/**
> +	 * @size: Length of the label, including the NULL terminator.
> +	 *
> +	 * Cannot be greater than the OS page size.
> +	 */
> +	__u32 size;
> +
> +	/** @label: User pointer to a NULL-terminated string */
> +	__u64 label;
> +};

First very minor NIT:
 * NULL is a pointer, i.e. (void*)0
 * NUL is the ASCII code point '\0'.
So it's a NUL-terminated string.

Second NIT: We don't actually need 'size' - since the string is
NUL-terminated we can just strndup_user(__user_pointer__, PAGE_SIZE).
As things stand we validate that strlen(label) < size <= PAGE_SIZE -
which is a little odd (user space might as well just pass PAGE_SIZE
rather than calculate the actual length).

Thanks,
Steve

> +
>  /**
>   * DRM_IOCTL_PANTHOR() - Build a Panthor IOCTL number
>   * @__access: Access type. Must be R, W or RW.
> @@ -1019,6 +1040,8 @@ enum {
>  		DRM_IOCTL_PANTHOR(WR, TILER_HEAP_CREATE, tiler_heap_create),
>  	DRM_IOCTL_PANTHOR_TILER_HEAP_DESTROY =
>  		DRM_IOCTL_PANTHOR(WR, TILER_HEAP_DESTROY, tiler_heap_destroy),
> +	DRM_IOCTL_PANTHOR_BO_SET_LABEL =
> +		DRM_IOCTL_PANTHOR(WR, BO_SET_LABEL, bo_set_label),
>  };
>  
>  #if defined(__cplusplus)