I/O memory access and hardware page mappings

Paul Boddie paul at boddie.org.uk
Wed Jul 26 00:42:17 CEST 2017


On Tuesday 25. July 2017 23.47.26 Adam Lackorzynski wrote:
> 
> There's no mechanism here that handles MMIO region sizes smaller than
> page size. Rather, l4io_request_iomem and friends to not handle
> addresses with offsets very well. Obviously I'll fix this.
> For now, please just use page-aligned physical addresses (and size).

Thanks for the information, Adam!

I thought that there might be some clever mechanism that filters accesses, but 
given that this probably can't be done without incurring any cost, I guess it 
isn't really feasible. Obviously, accesses purely employing the hardware 
mapping mechanism are desirable, even for potentially low-bandwidth activities 
like setting GPIO pins.

I did wonder how I might work with the return values from l4io_request_iomem 
and related functions, but I couldn't figure that out.

Paul



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