Messages in this thread | | | Date | Sat, 31 Jul 2021 00:42:34 +0800 | From | Boqun Feng <> | Subject | [Question] Alignment requirement for readX() and writeX() |
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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
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