[PATCH v10 2/7] ARM: hi3xxx: add board support with device tree

[arnd@arndb.de (Arnd Bergmann)]

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