On Wednesday 16 October 2013, Haojian Zhuang wrote:
> Oh, no. I shouldn't extend the static mapping table to the entire range.
>
> Most of the registers only need to map once in the probe() function
> of the driver. Whether it's using static mapping or dynamic mapping,
> there's no difference.
There is a small difference in that having a megabyte-sized mapping will
reduce the number of TLB entries required for I/O access, which can
improve performance slightly. Other platforms do it for this reason.
> The sysctrl register bank is used in both clock & platform
> driver. Each clock node contains reg property, it needs to be parsed
> by of_iomap(). Hotplug & SMP platform driver needs to parse sysctrl
> register bank also. If I don't choose the static IO mapping for sysctrl
> register bank, I have to define some global variable to store the
> virtual address mapping. Or I have to cost lots of redundant virtual
> address space for the same IO mapping.
It's a small cost, but your approach makes sense, just make sure
you have a comment in the map_io code explaining it.
> So I'll only keep the static IO mapping for sysctrl.
I'd still choose the larger mapping, but I'll leave the decision to you.
Arnd
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