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Date:   Wed, 5 Apr 2023 16:44:13 +0200
From:   Daniel Vetter <daniel@ffwll.ch>
To:     Asahi Lina <lina@asahilina.net>
Cc:     Maarten Lankhorst <maarten.lankhorst@linux.intel.com>,
        Maxime Ripard <mripard@kernel.org>,
        Thomas Zimmermann <tzimmermann@suse.de>,
        David Airlie <airlied@gmail.com>,
        Daniel Vetter <daniel@ffwll.ch>,
        Miguel Ojeda <ojeda@kernel.org>,
        Alex Gaynor <alex.gaynor@gmail.com>,
        Wedson Almeida Filho <wedsonaf@gmail.com>,
        Boqun Feng <boqun.feng@gmail.com>, Gary Guo <gary@garyguo.net>,
        =?iso-8859-1?Q?Bj=F6rn?= Roy Baron <bjorn3_gh@protonmail.com>,
        Sumit Semwal <sumit.semwal@linaro.org>,
        Christian =?iso-8859-1?Q?K=F6nig?= <christian.koenig@amd.com>,
        Luben Tuikov <luben.tuikov@amd.com>,
        Jarkko Sakkinen <jarkko@kernel.org>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Alyssa Rosenzweig <alyssa@rosenzweig.io>,
        Karol Herbst <kherbst@redhat.com>,
        Ella Stanforth <ella@iglunix.org>,
        Faith Ekstrand <faith.ekstrand@collabora.com>,
        Mary <mary@mary.zone>, linux-kernel@vger.kernel.org,
        dri-devel@lists.freedesktop.org, rust-for-linux@vger.kernel.org,
        linux-media@vger.kernel.org, linaro-mm-sig@lists.linaro.org,
        linux-sgx@vger.kernel.org, asahi@lists.linux.dev
Subject: Re: [PATCH RFC 18/18] drm/asahi: Add the Asahi driver for Apple AGX
 GPUs
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        Maarten Lankhorst <maarten.lankhorst@linux.intel.com>,
        Maxime Ripard <mripard@kernel.org>,
        Thomas Zimmermann <tzimmermann@suse.de>,
        David Airlie <airlied@gmail.com>, Miguel Ojeda <ojeda@kernel.org>,
        Alex Gaynor <alex.gaynor@gmail.com>,
        Wedson Almeida Filho <wedsonaf@gmail.com>,
        Boqun Feng <boqun.feng@gmail.com>, Gary Guo <gary@garyguo.net>,
        =?iso-8859-1?Q?Bj=F6rn?= Roy Baron <bjorn3_gh@protonmail.com>,
        Sumit Semwal <sumit.semwal@linaro.org>,
        Christian =?iso-8859-1?Q?K=F6nig?= <christian.koenig@amd.com>,
        Luben Tuikov <luben.tuikov@amd.com>,
        Jarkko Sakkinen <jarkko@kernel.org>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Alyssa Rosenzweig <alyssa@rosenzweig.io>,
        Karol Herbst <kherbst@redhat.com>,
        Ella Stanforth <ella@iglunix.org>,
        Faith Ekstrand <faith.ekstrand@collabora.com>,
        Mary <mary@mary.zone>, linux-kernel@vger.kernel.org,
        dri-devel@lists.freedesktop.org, rust-for-linux@vger.kernel.org,
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        linux-sgx@vger.kernel.org, asahi@lists.linux.dev
References: <20230307-rust-drm-v1-0-917ff5bc80a8@asahilina.net>
 <20230307-rust-drm-v1-18-917ff5bc80a8@asahilina.net>
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In-Reply-To: <20230307-rust-drm-v1-18-917ff5bc80a8@asahilina.net>
Precedence: bulk

On Tue, Mar 07, 2023 at 11:25:43PM +0900, Asahi Lina wrote:
> +/// Look up a GEM object handle for a `File` and return an `ObjectRef` for it.
> +pub(crate) fn lookup_handle(file: &DrmFile, handle: u32) -> Result<ObjectRef> {
> +    Ok(ObjectRef::new(shmem::Object::lookup_handle(file, handle)?))
> +}

So maybe my expectations for rust typing is a bit too much, but I kinda
expected this to be fully generic:

- trait Driver (drm_driver) knows the driver's object type
- a generic create_handle function could ensure that for drm_file (which
  is always for a specific drm_device and hence Driver) can ensure at the
  type level that you only put the right objects into the drm_file
- a generic lookup_handle function on the drm_file knows the Driver trait
  and so can give you back the right type right away.

Why the wrapping, what do I miss?
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch