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

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Message-Id: <260D98E1-7204-4535-A84F-D55A4527FF7E@collabora.com>
Date: Sun, 23 Mar 2025 21:20:28 -0300
From: Daniel Almeida <daniel.almeida@...labora.com>
To: Alyssa Rosenzweig <alyssa@...enzweig.io>
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

Hi Alyssa,

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

— Daniel