From: Laura Nao <laura.nao@collabora.com>
To: gary@garyguo.net
Cc: a.hindborg@kernel.org, acourbot@nvidia.com, airlied@gmail.com,
aliceryhl@google.com, anna-maria@linutronix.de,
bjorn3_gh@protonmail.com, boqun@kernel.org, dakr@kernel.org,
daniel.almeida@collabora.com, dri-devel@lists.freedesktop.org,
driver-core@lists.linux.dev, frederic@kernel.org,
fujita.tomonori@gmail.com, jstultz@google.com,
kernel@collabora.com, laura.nao@collabora.com,
linux-kernel@vger.kernel.org, lossin@kernel.org,
lyude@redhat.com, ojeda@kernel.org,
rust-for-linux@vger.kernel.org, sboyd@kernel.org,
simona@ffwll.ch, tamird@kernel.org, tglx@kernel.org,
tmgross@umich.edu, work@onurozkan.dev
Subject: Re: [PATCH 2/9] rust: io: drop the CONFIG_64BIT restriction on system memory u64 access
Date: Mon, 21 Sep 2026 12:06:41 +0200 [thread overview]
Message-ID: <20260921100641.228824-1-laura.nao@collabora.com> (raw)
In-Reply-To: <DLFUKN84E2XS.33S0LZHBMAWH2@garyguo.net>
Hi Gary,
On 9/15/26 13:18, Gary Guo wrote:
> On Tue Sep 15, 2026 at 11:57 AM BST, Laura Nao wrote:
>> SysMemBackend's IoCapable<u64> impl is currently gated on CONFIG_64BIT,
>> copying the MMIO backend's restriction. MMIO needs that gate because
>> readq() is not available on 32bit. System memory has no such dependency:
>> a u64 volatile load/store compiles on any architecture, it's just not
>> single-copy atomic on 32bit.
>>
>> Drop the gate so u64-backed types, such as bitfields, work on 32bit too.
>> Document the non-atomicity at the impl instead of enforcing it at build
>> time.
>>
>> Co-developed-by: Daniel Almeida <daniel.almeida@collabora.com>
>> Signed-off-by: Daniel Almeida <daniel.almeida@collabora.com>
>> Signed-off-by: Laura Nao <laura.nao@collabora.com>
>
> No. If you don't need atomicity, please use `copy_read` to read the value. It'll
> compile down to the same volatile read, just without atomicity guarantee.
>
Ack, thanks for the feedback. I'll drop this in v2.
Best,
Laura
next prev parent reply other threads:[~2026-09-21 10:06 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-09-15 10:57 [PATCH 0/9] drm/tyr: add CSF firmware interface support Laura Nao
2026-09-15 10:57 ` [PATCH 1/9] drm/tyr: validate presence of CSF shared section Laura Nao
2026-09-23 13:59 ` Daniel Almeida
2026-09-15 10:57 ` [PATCH 2/9] rust: io: drop the CONFIG_64BIT restriction on system memory u64 access Laura Nao
2026-09-15 11:18 ` Gary Guo
2026-09-21 10:06 ` Laura Nao [this message]
2026-09-15 10:57 ` [PATCH 3/9] drm/tyr: add MappedBo, a kernel BO with an always-valid CPU mapping Laura Nao
2026-09-23 20:43 ` Daniel Almeida
2026-09-15 10:57 ` [PATCH 4/9] drm/tyr: add McuVa and claim-checked MappedBo views Laura Nao
2026-09-23 20:42 ` Daniel Almeida
2026-09-15 10:57 ` [PATCH 5/9] drm/tyr: drop unused KernelBo::bo() function Laura Nao
2026-09-23 20:45 ` Daniel Almeida
2026-09-15 10:57 ` [PATCH 6/9] drm/tyr: add CSF firmware interface support Laura Nao
2026-09-26 0:24 ` Daniel Almeida
2026-09-15 10:57 ` [PATCH 7/9] rust: time: add arch_timer_get_rate wrapper Laura Nao
2026-09-22 12:57 ` Andreas Hindborg
2026-09-22 14:23 ` FUJITA Tomonori
2026-09-22 19:56 ` Gary Guo
2026-09-15 10:57 ` [PATCH 8/9] drm/tyr: program CSF global interface Laura Nao
2026-09-15 10:57 ` [PATCH 9/9] drm/tyr: wait for global interface readiness Laura Nao
2026-09-23 8:50 ` Alice Ryhl
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