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From: Alyssa Rosenzweig <alyssa@rosenzweig.io>
To: Daniel Almeida <daniel.almeida@collabora.com>
Cc: Faith Ekstrand <faith.ekstrand@collabora.com>,
	David Airlie <airlied@gmail.com>, Simona Vetter <simona@ffwll.ch>,
	Maarten Lankhorst <maarten.lankhorst@linux.intel.com>,
	Maxime Ripard <mripard@kernel.org>,
	Thomas Zimmermann <tzimmermann@suse.de>,
	Miguel Ojeda <ojeda@kernel.org>,
	Alex Gaynor <alex.gaynor@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>,
	Benno Lossin <benno.lossin@proton.me>,
	Andreas Hindborg <a.hindborg@kernel.org>,
	Alice Ryhl <aliceryhl@google.com>, Trevor Gross <tmgross@umich.edu>,
	Janne Grunau <j@jannau.net>, Sven Peter <sven@svenpeter.dev>,
	Jonathan Corbet <corbet@lwn.net>,
	Sergio Lopez Pascual <slp@sinrega.org>,
	Ryan Houdek <sonicadvance1@gmail.com>,
	linux-kernel <linux-kernel@vger.kernel.org>,
	dri-devel <dri-devel@lists.freedesktop.org>,
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	asahi <asahi@lists.linux.dev>,
	linux-arm-kernel <linux-arm-kernel@lists.infradead.org>,
	linux-doc <linux-doc@vger.kernel.org>,
	Asahi Lina <lina@asahilina.net>
Subject: Re: [PATCH v3] drm: Add UAPI for the Asahi driver
Message-ID: <Z-Fn4niI6_Yd06Ze@blossom>
References: <20250314-agx-uapi-v3-1-3abf7e74ea2f@rosenzweig.io>
 <195b507d4b3.b25d0dad175771.7566427576910952468@collabora.com>
 <195b582682b.121ba4d5e219032.3109114844776468245@collabora.com>
 <Z-B6uc7EEAdBPXmt@blossom>
 <260D98E1-7204-4535-A84F-D55A4527FF7E@collabora.com>
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> >>>> +    /** 
> >>>> +     * @DRM_ASAHI_BIND_SINGLE_PAGE: Map a single page of the BO repeatedly 
> >>>> +     * across the VA range. 
> >>>> +     * 
> >>>> +     * This is useful to fill a VA range with scratch pages or zero pages. 
> >>>> +     * It is intended as a mechanism to accelerate sparse. 
> >>>> +     */ 
> >>>> +    DRM_ASAHI_BIND_SINGLE_PAGE = (1L << 2),
> >> 
> >> Does this require the BO to be a single page? If so, does it require offset==0? Or does it just take whatever page is at the specified offset?
> > 
> > I believe the intention is that it takes whatever page is at the
> > specified offset and just maps that a bunch of times. HK doesn't use
> > this yet though it probably should (this was added to help reduce
> > overhead when emulating sparse with scratch/zero pages, which is still
> > very new functionality in hk).
> > 
> > Accelerating this properly involves GPUVM patches - although even without
> > that, moving the loop into the kernel so it's only a single ioctl
> > (user-kernel roundtrip) seems worth keeping the flag for.
> 
> FYI: I will be posting a patch for the GPUVM abstraction soon.

Great to hear :) Although in this case, I meant that accelerating
DRM_ASAHI_BIND_SINGLE_PAGE requires patches to extend the actual C
implementation of drm/gpuvm, not just the Rust abstraction. Which is a
bit annoying for non-essential functionality with regards to upstreaming
things...