linux-kernel - Re: [PATCH 06/11] io: move PIO

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Message-Id: <13e23d59-ca5d-4cc7-83cd-0c3f41b1bedc@app.fastmail.com>
Date: Fri, 09 May 2025 07:42:05 +0200
From: "Arnd Bergmann" <arnd@...db.de>
To: "Andrew Ballance" <andrewjballance@...il.com>,
 "Danilo Krummrich" <dakr@...nel.org>, "Dave Airlie" <airlied@...il.com>,
 "Simona Vetter" <simona@...ll.ch>,
 "Andrew Morton" <akpm@...ux-foundation.org>,
 "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>,
 "Greg Kroah-Hartman" <gregkh@...uxfoundation.org>,
 "Rafael J . Wysocki" <rafael@...nel.org>, bhelgaas@...gle.com,
 Krzysztof Wilczyński <kwilczynski@...nel.org>,
 "Raag Jadav" <raag.jadav@...el.com>,
 "Andy Shevchenko" <andriy.shevchenko@...ux.intel.com>, me@...enk.dev,
 "FUJITA Tomonori" <fujita.tomonori@...il.com>, daniel.almeida@...labora.com
Cc: "nouveau@...ts.freedesktop.org" <nouveau@...ts.freedesktop.org>,
 dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
 rust-for-linux@...r.kernel.org, linux-pci@...r.kernel.org
Subject: Re: [PATCH 06/11] io: move PIO_OFFSET to linux/io.h

On Fri, May 9, 2025, at 05:15, Andrew Ballance wrote:
> From: Fiona Behrens <me@...enk.dev>
>
> Move the non arch specific PIO size to linux/io.h.
>
> This allows rust to access `PIO_OFFSET`, `PIO_MASK` and
> `PIO_RESERVED`. This is required to implement `IO_COND` in rust.
>
> Signed-off-by: Fiona Behrens <me@...enk.dev>
> Signed-off-by: Andrew Ballance <andrewjballance@...il.com>

This puts an implementation detail of the x86 specific
iomap() code (unfortunately named "GENERIC_IOMAP" for historic
reasons) into common code. Please don't do that.

We still have a couple of users of GENERIC_IOMAP outside of
x86, but they all work in subtly different ways, and I've
been thinking about better ways to handle those. Ideally
the nonstandard iomap variants (x86, uml, powerpc/powernv,
m68k/q40) should just implement their own ioread/iowrite
helpers out-of-line like we do on alpha and parisc, while
everyone else just aliases them to readl/writel.

      Arnd