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Doesn't pos need to be aligned to 32bit as well (at least at actually reading from iomem)?

Good point, we can either return an error if the count in both a multiple of 32 bits, or do some caching to allow for arbitrary size access. The former is very simple but not sure if this is accepted behavior for debugfs.

You really want something that will work with arbatrary userspace tools if you can rather than requiring special magic read sizes - things like cat and cp should probably work. A common thing is to do reads/writes of the correct sizes into a buffer and then pick the relevant bits out of the buffer to satisfy what userspace actually asked for.

Thanks for the advice. The data is already in a buffer so it's not difficult to implement support for sizes that aren't multiple of 4 bytes.