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From: Boqun Feng <boqun.feng@gmail.com>
To: linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org
Cc: Miguel Ojeda <miguel.ojeda.sandonis@gmail.com>,
	Wedson Almeida Filho <wedsonaf@google.com>,
	Gary Guo <gary@garyguo.net>, Hector Martin <marcan@marcan.st>,
	Arnd Bergmann <arnd@arndb.de>,
	Linus Walleij <linus.walleij@linaro.org>
Subject: [Question] Alignment requirement for readX() and writeX()
Date: Sat, 31 Jul 2021 00:42:34 +0800	[thread overview]
Message-ID: <YQQr+twAYHk2jXs6@boqun-archlinux> (raw)

Hi,

The background is that I'm reviewing Wedson's PR on IoMem for
Rust-for-Linux project:
	
	https://github.com/Rust-for-Linux/linux/pull/462

readX() and writeX() are used to provide Rust code to read/write IO
memory. And I want to find whether we need to check the alignment of the
pointer. I wonder whether the addresses passed to readX() and writeX()
need to be aligned to the size of the accesses (e.g. the parameter of
readl() has to be a 4-byte aligned pointer).

The only related information I get so far is the following quote in
Documentation/driver-io/device-io.rst:

	On many platforms, I/O accesses must be aligned with respect to
	the access size; failure to do so will result in an exception or
	unpredictable results.

Does it mean all readX() and writeX() need to use aligned addresses?
Or the alignment requirement is arch-dependent, i.e. if the architecture
supports and has enabled misalignment load and store, no alignment
requirement on readX() and writeX(), otherwise still need to use aligned
addresses.

I know different archs have their own alignment requirement on memory
accesses, just want to make sure the requirement of the readX() and
writeX() APIs.

Thanks a lot!

Regards,
Boqun

             reply	other threads:[~2021-07-30 16:43 UTC|newest]

Thread overview: 6+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-07-30 16:42 Boqun Feng [this message]
2021-07-30 16:58 ` Arnd Bergmann
2021-07-30 17:30   ` Boqun Feng
2021-07-30 20:24     ` Arnd Bergmann
2021-07-31  1:51       ` Boqun Feng
2021-08-02  8:37   ` David Laight

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