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

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Message-ID: <sscuzi4asw627u5mnj5bsc4cgxfcpfsbgfpod4v3ft3bfs7wbf@fsubfgttprnb>
Date: Wed, 7 May 2025 15:12:57 +0100
From: Adrián Larumbe <adrian.larumbe@...labora.com>
To: Steven Price <steven.price@....com>
Cc: linux-kernel@...r.kernel.org, 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 07.05.2025 14:18, Steven Price wrote:
> 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"?
>
That's right, that was only the case in Panthor when labelling kernel BOs.
Since all GEM BO's in Panfrost are user-facing, there's no need to label
any 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__ */

Adrian Larumbe