linux-kernel - Re: [PATCH 1/3] drm/panfrost: Add BO labelling to Panfrost

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Message-ID: <24ee069c-b66a-4810-b8aa-4aa88d8fdab4@arm.com>
Date: Wed, 7 May 2025 14:18:30 +0100
From: Steven Price <steven.price@....com>
To: Adrián Larumbe <adrian.larumbe@...labora.com>,
 linux-kernel@...r.kernel.org
Cc: dri-devel@...ts.freedesktop.org,
 Boris Brezillon <boris.brezillon@...labora.com>, kernel@...labora.com,
 Rob Herring <robh@...nel.org>,
 Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
 Maxime Ripard <mripard@...nel.org>, Thomas Zimmermann <tzimmermann@...e.de>,
 David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>
Subject: Re: [PATCH 1/3] drm/panfrost: Add BO labelling to Panfrost

On 24/04/2025 03:21, Adrián Larumbe wrote:
> Unlike in Panthor, from where this change is based on, there is no need
> to support tagging of BO's other than UM-exposed ones, so all strings
> can be freed with kfree().
> 
> This commit is done in preparation of a following one that will allow
> UM to set BO labels through a new ioctl().
> 
> Signed-off-by: Adrián Larumbe <adrian.larumbe@...labora.com>

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

But one comment below

> ---
>  drivers/gpu/drm/panfrost/panfrost_gem.c | 19 +++++++++++++++++++
>  drivers/gpu/drm/panfrost/panfrost_gem.h | 16 ++++++++++++++++
>  2 files changed, 35 insertions(+)
> 
> diff --git a/drivers/gpu/drm/panfrost/panfrost_gem.c b/drivers/gpu/drm/panfrost/panfrost_gem.c
> index 963f04ba2de6..a7a29974d8b1 100644
> --- a/drivers/gpu/drm/panfrost/panfrost_gem.c
> +++ b/drivers/gpu/drm/panfrost/panfrost_gem.c
> @@ -1,6 +1,7 @@
>  // SPDX-License-Identifier: GPL-2.0
>  /* Copyright 2019 Linaro, Ltd, Rob Herring <robh@...nel.org> */
>  
> +#include <linux/cleanup.h>
>  #include <linux/err.h>
>  #include <linux/slab.h>
>  #include <linux/dma-buf.h>
> @@ -35,6 +36,9 @@ static void panfrost_gem_free_object(struct drm_gem_object *obj)
>  	 */
>  	WARN_ON_ONCE(!list_empty(&bo->mappings.list));
>  
> +	kfree(bo->label.str);
> +	mutex_destroy(&bo->label.lock);
> +
>  	if (bo->sgts) {
>  		int i;
>  		int n_sgt = bo->base.base.size / SZ_2M;
> @@ -260,6 +264,7 @@ struct drm_gem_object *panfrost_gem_create_object(struct drm_device *dev, size_t
>  	mutex_init(&obj->mappings.lock);
>  	obj->base.base.funcs = &panfrost_gem_funcs;
>  	obj->base.map_wc = !pfdev->coherent;
> +	mutex_init(&obj->label.lock);
>  
>  	return &obj->base.base;
>  }
> @@ -302,3 +307,17 @@ panfrost_gem_prime_import_sg_table(struct drm_device *dev,
>  
>  	return obj;
>  }
> +
> +void
> +panfrost_gem_set_label(struct drm_gem_object *obj, const char *label)
> +{
> +	struct panfrost_gem_object *bo = to_panfrost_bo(obj);
> +	const char *old_label;
> +
> +	scoped_guard(mutex, &bo->label.lock) {
> +		old_label = bo->label.str;
> +		bo->label.str = label;
> +	}
> +
> +	kfree(old_label);
> +}
> diff --git a/drivers/gpu/drm/panfrost/panfrost_gem.h b/drivers/gpu/drm/panfrost/panfrost_gem.h
> index 7516b7ecf7fe..c0be2934f229 100644
> --- a/drivers/gpu/drm/panfrost/panfrost_gem.h
> +++ b/drivers/gpu/drm/panfrost/panfrost_gem.h
> @@ -41,6 +41,20 @@ struct panfrost_gem_object {
>  	 */
>  	size_t heap_rss_size;
>  
> +	/**
> +	 * @label: BO tagging fields. The label can be assigned within the
> +	 * driver itself or through a specific IOCTL.

>From the commit message (about the use of kfree()) I assume we are not
expecting this to be assigned "within the driver itself"?

Thanks,
Steve

> +	 */
> +	struct {
> +		/**
> +		 * @label.str: Pointer to NULL-terminated string,
> +		 */
> +		const char *str;
> +
> +		/** @lock.str: Protects access to the @label.str field. */
> +		struct mutex lock;
> +	} label;
> +
>  	bool noexec		:1;
>  	bool is_heap		:1;
>  };
> @@ -89,4 +103,6 @@ void panfrost_gem_teardown_mappings_locked(struct panfrost_gem_object *bo);
>  int panfrost_gem_shrinker_init(struct drm_device *dev);
>  void panfrost_gem_shrinker_cleanup(struct drm_device *dev);
>  
> +void panfrost_gem_set_label(struct drm_gem_object *obj, const char *label);
> +
>  #endif /* __PANFROST_GEM_H__ */