Re: [PATCH v5 1/4] drm/panthor: Introduce BO labeling

[Boris Brezillon <boris.brezillon@collabora.com>]

On Tue,  8 Apr 2025 23:24:21 +0100
Adrián Larumbe <adrian.larumbe@collabora.com> wrote:

> Add a new character string Panthor BO field, and a function that allows
> setting it from within the driver.
> 
> Driver takes care of freeing the string when it's replaced or no longer
> needed at object destruction time, but allocating it is the responsibility
> of callers.
> 
> Signed-off-by: Adrián Larumbe <adrian.larumbe@collabora.com>

One minor thing below, but this looks good otherwise

Reviewed-by: Boris Brezillon <boris.brezillon@collabora.com>

> ---
>  drivers/gpu/drm/panthor/panthor_gem.c | 38 +++++++++++++++++++++++++++
>  drivers/gpu/drm/panthor/panthor_gem.h | 17 ++++++++++++
>  2 files changed, 55 insertions(+)
> 
> diff --git a/drivers/gpu/drm/panthor/panthor_gem.c b/drivers/gpu/drm/panthor/panthor_gem.c
> index 8244a4e6c2a2..7d017f9d1d52 100644
> --- a/drivers/gpu/drm/panthor/panthor_gem.c
> +++ b/drivers/gpu/drm/panthor/panthor_gem.c
> @@ -18,6 +18,14 @@ static void panthor_gem_free_object(struct drm_gem_object *obj)
>  	struct panthor_gem_object *bo = to_panthor_bo(obj);
>  	struct drm_gem_object *vm_root_gem = bo->exclusive_vm_root_gem;
>  
> +	/*
> +	 * Label might have been allocated with kstrdup_const(),
> +	 * we need to take that into account when freeing the memory
> +	 */
> +	kfree_const(bo->label.str);
> +
> +	mutex_destroy(&bo->label.lock);
> +
>  	drm_gem_free_mmap_offset(&bo->base.base);
>  	mutex_destroy(&bo->gpuva_list_lock);
>  	drm_gem_shmem_free(&bo->base);
> @@ -196,6 +204,7 @@ struct drm_gem_object *panthor_gem_create_object(struct drm_device *ddev, size_t
>  	obj->base.map_wc = !ptdev->coherent;
>  	mutex_init(&obj->gpuva_list_lock);
>  	drm_gem_gpuva_set_lock(&obj->base.base, &obj->gpuva_list_lock);
> +	mutex_init(&obj->label.lock);
>  
>  	return &obj->base.base;
>  }
> @@ -247,3 +256,32 @@ panthor_gem_create_with_handle(struct drm_file *file,
>  
>  	return ret;
>  }
> +
> +void
> +panthor_gem_bo_set_label(struct drm_gem_object *obj, const char *label)
> +{
> +	struct panthor_gem_object *bo = to_panthor_bo(obj);
> +	const char *old_label;
> +
> +	mutex_lock(&bo->label.lock);
> +	old_label = bo->label.str;
> +	bo->label.str = label;
> +	mutex_unlock(&bo->label.lock);

Since you started using scoped_guard, maybe use it here too:

	scoped_guard(mutex, &bo->label.lock) {
		old_label = bo->label.str;
		bo->label.str = label;
	}

> +
> +	kfree(old_label);
> +}
> +
> +void
> +panthor_gem_kernel_bo_set_label(struct panthor_kernel_bo *bo, const char *label)
> +{
> +	const char *str;
> +
> +	str = kstrdup_const(label, GFP_KERNEL);
> +	if (!str) {
> +		/* Failing to allocate memory for a label isn't a fatal condition */
> +		drm_warn(bo->obj->dev, "Not enough memory to allocate BO label");
> +		return;
> +	}
> +
> +	panthor_gem_bo_set_label(bo->obj, kstrdup_const(str, GFP_KERNEL));
> +}
> diff --git a/drivers/gpu/drm/panthor/panthor_gem.h b/drivers/gpu/drm/panthor/panthor_gem.h
> index 5749ef2ebe03..0582826b341a 100644
> --- a/drivers/gpu/drm/panthor/panthor_gem.h
> +++ b/drivers/gpu/drm/panthor/panthor_gem.h
> @@ -46,6 +46,20 @@ struct panthor_gem_object {
>  
>  	/** @flags: Combination of drm_panthor_bo_flags flags. */
>  	u32 flags;
> +
> +	/**
> +	 * @label: BO tagging fields. The label can be assigned within the
> +	 * driver itself or through a specific IOCTL.
> +	 */
> +	struct {
> +		/**
> +		 * @label.str: Pointer to NULL-terminated string,
> +		 */
> +		const char *str;
> +
> +		/** @lock.str: Protects access to the @label.str field. */
> +		struct mutex lock;
> +	} label;
>  };
>  
>  /**
> @@ -91,6 +105,9 @@ panthor_gem_create_with_handle(struct drm_file *file,
>  			       struct panthor_vm *exclusive_vm,
>  			       u64 *size, u32 flags, uint32_t *handle);
>  
> +void panthor_gem_bo_set_label(struct drm_gem_object *obj, const char *label);
> +void panthor_gem_kernel_bo_set_label(struct panthor_kernel_bo *bo, const char *label);
> +
>  static inline u64
>  panthor_kernel_bo_gpuva(struct panthor_kernel_bo *bo)
>  {