linux-kernel - Re: [PATCH v3] drm: Add UAPI for the Asahi driver

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Message-ID: <Z-Fn4niI6_Yd06Ze@blossom>
Date: Mon, 24 Mar 2025 10:10:42 -0400
From: Alyssa Rosenzweig <alyssa@...enzweig.io>
To: Daniel Almeida <daniel.almeida@...labora.com>
Cc: Faith Ekstrand <faith.ekstrand@...labora.com>,
	David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>,
	Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
	Maxime Ripard <mripard@...nel.org>,
	Thomas Zimmermann <tzimmermann@...e.de>,
	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>,
	Janne Grunau <j@...nau.net>, Sven Peter <sven@...npeter.dev>,
	Jonathan Corbet <corbet@....net>,
	Sergio Lopez Pascual <slp@...rega.org>,
	Ryan Houdek <sonicadvance1@...il.com>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	dri-devel <dri-devel@...ts.freedesktop.org>,
	rust-for-linux <rust-for-linux@...r.kernel.org>,
	asahi <asahi@...ts.linux.dev>,
	linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
	linux-doc <linux-doc@...r.kernel.org>,
	Asahi Lina <lina@...hilina.net>
Subject: Re: [PATCH v3] drm: Add UAPI for the Asahi driver

> >>>> +    /** 
> >>>> +     * @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...