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Date: Sat, 20 Sep 2025 01:56:27 +0200
Message-Id: <DCX6M3BCXV2W.37USDZEDRVA2G@kernel.org>
Subject: Re: [PATCH] rust: io: use const generics for read/write offsets
Cc: "Joel Fernandes" <joelagnelf@nvidia.com>, "Alice Ryhl"
 <aliceryhl@google.com>, "Maarten Lankhorst"
 <maarten.lankhorst@linux.intel.com>, "Maxime Ripard" <mripard@kernel.org>,
 "Thomas Zimmermann" <tzimmermann@suse.de>, "David Airlie"
 <airlied@gmail.com>, "Simona Vetter" <simona@ffwll.ch>, "Greg
 Kroah-Hartman" <gregkh@linuxfoundation.org>, "Rafael J. Wysocki"
 <rafael@kernel.org>, "Miguel Ojeda" <ojeda@kernel.org>, "Boqun Feng"
 <boqun.feng@gmail.com>, =?utf-8?q?Bj=C3=B6rn_Roy_Baron?=
 <bjorn3_gh@protonmail.com>, "Benno Lossin" <lossin@kernel.org>, "Andreas
 Hindborg" <a.hindborg@kernel.org>, "Trevor Gross" <tmgross@umich.edu>,
 "Bjorn Helgaas" <bhelgaas@google.com>,
 =?utf-8?q?Krzysztof_Wilczy=C5=84ski?= <kwilczynski@kernel.org>,
 <linux-kernel@vger.kernel.org>, <rust-for-linux@vger.kernel.org>,
 <dri-devel@lists.freedesktop.org>, <linux-pci@vger.kernel.org>
To: "Gary Guo" <gary@garyguo.net>
From: "Danilo Krummrich" <dakr@kernel.org>
References: <20250918-write-offset-const-v1-1-eb51120d4117@google.com>
 <20250918181357.GA1825487@joelbox2> <DCWBCL9U0IY4.NFNUMLRULAWM@kernel.org>
 <20250919215634.7a1c184e.gary@garyguo.net>
In-Reply-To: <20250919215634.7a1c184e.gary@garyguo.net>

On Fri Sep 19, 2025 at 10:56 PM CEST, Gary Guo wrote:
> Turbofish is cumbersome to write with just magic numbers, and the
> fact `{}` is needed to pass in constant expressions made this much
> worse. If the drivers try hard to avoid magic numbers, you would
> effective require  all code to be `::<{ ... }>()` and this is ugly.

In the absolute majority of cases users won't see any of that anyways, sinc=
e
they'll use the register!() macro generated types.

   // Master Control Register (MCR)
   //
   // Stores the offset as associated constant.
   let mcr =3D regs::MCR::default();

   // Set the enabled bit.
   mcr.enable();

   // Write the data on the bus.
   //
   // Calls `io.write<Self::OFFSET>(self.data())` internally.
   mcr.write(&io);

For indexed registers it is indeed a problem though.