linux-kernel - Re: [PATCH 5/7] drm/gem: Add a flag to control whether objects can be exported

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Message-ID: <0d6f762f-a5c7-47e2-8fac-b946b090f2f9@amd.com>
Date: Wed, 19 Mar 2025 09:04:42 +0100
From: Christian König <christian.koenig@....com>
To: Daniel Almeida <daniel.almeida@...labora.com>,
 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>,
 Miguel Ojeda <ojeda@...nel.org>, Alex Gaynor <alex.gaynor@...il.com>,
 Boqun Feng <boqun.feng@...il.com>, Gary Guo <gary@...yguo.net>,
 Björn Roy Baron <bjorn3_gh@...tonmail.com>,
 Benno Lossin <benno.lossin@...ton.me>,
 Andreas Hindborg <a.hindborg@...nel.org>, Alice Ryhl <aliceryhl@...gle.com>,
 Trevor Gross <tmgross@...ch.edu>, Sumit Semwal <sumit.semwal@...aro.org>
Cc: dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
 rust-for-linux@...r.kernel.org, linux-media@...r.kernel.org,
 linaro-mm-sig@...ts.linaro.org, Danilo Krummrich <dakr@...nel.org>,
 Asahi Lina <lina@...hilina.net>
Subject: Re: [PATCH 5/7] drm/gem: Add a flag to control whether objects can be
 exported

Am 18.03.25 um 20:22 schrieb Daniel Almeida:
> From: Asahi Lina <lina@...hilina.net>
>
> Drivers may want to support driver-private objects, which cannot be
> shared. This allows them to share a single lock and enables other
> optimizations.
>
> Add an `exportable` field to drm_gem_object, which blocks PRIME export
> if set to false. It is initialized to true in
> drm_gem_private_object_init.

We already have a method for doing that which is used by almost all drivers (except for lsdc).

Basically you just create a function which checks the per-requisites if a buffer can be exported before calling drm_gem_prime_export() and installs that as .export callback into the drm_gem_object_funcs.

See amdgpu_gem_prime_export() for a simpler example.

Regards,
Christian.

>
> Signed-off-by: Asahi Lina <lina@...hilina.net>
> Signed-off-by: Daniel Almeida <daniel.almeida@...labora.com>
> ---
>  drivers/gpu/drm/drm_gem.c   | 1 +
>  drivers/gpu/drm/drm_prime.c | 5 +++++
>  include/drm/drm_gem.h       | 8 ++++++++
>  3 files changed, 14 insertions(+)
>
> diff --git a/drivers/gpu/drm/drm_gem.c b/drivers/gpu/drm/drm_gem.c
> index ee811764c3df4b4e9c377a66afd4967512ba2001..8f998fe6beecd285ce3e2d5badfa95eb7d7bd548 100644
> --- a/drivers/gpu/drm/drm_gem.c
> +++ b/drivers/gpu/drm/drm_gem.c
> @@ -195,6 +195,7 @@ void drm_gem_private_object_init(struct drm_device *dev,
>  
>  	drm_vma_node_reset(&obj->vma_node);
>  	INIT_LIST_HEAD(&obj->lru_node);
> +	obj->exportable = true;
>  }
>  EXPORT_SYMBOL(drm_gem_private_object_init);
>  
> diff --git a/drivers/gpu/drm/drm_prime.c b/drivers/gpu/drm/drm_prime.c
> index 32a8781cfd67b82ece7b7b94625715171bb41917..20aa350280abe9a6ed6742e131ff50c65bc9dfa9 100644
> --- a/drivers/gpu/drm/drm_prime.c
> +++ b/drivers/gpu/drm/drm_prime.c
> @@ -387,6 +387,11 @@ static struct dma_buf *export_and_register_object(struct drm_device *dev,
>  		return dmabuf;
>  	}
>  
> +	if (!obj->exportable) {
> +		dmabuf = ERR_PTR(-EINVAL);
> +		return dmabuf;
> +	}
> +
>  	if (obj->funcs && obj->funcs->export)
>  		dmabuf = obj->funcs->export(obj, flags);
>  	else
> diff --git a/include/drm/drm_gem.h b/include/drm/drm_gem.h
> index fdae947682cd0b7b06db5e35e120f049a0f30179..f700e4996eccb92597cca6b8c3df8e35b864c1e1 100644
> --- a/include/drm/drm_gem.h
> +++ b/include/drm/drm_gem.h
> @@ -432,6 +432,14 @@ struct drm_gem_object {
>  	 * The current LRU list that the GEM object is on.
>  	 */
>  	struct drm_gem_lru *lru;
> +
> +	/**
> +	 * @exportable:
> +	 *
> +	 * Whether this GEM object can be exported via the drm_gem_object_funcs->export
> +	 * callback. Defaults to true.
> +	 */
> +	bool exportable;
>  };
>  
>  /**
>