On Wed, 29 Oct 2014, Arnd Bergmann wrote:
> On Wednesday 29 October 2014 13:09:47 Kevin Cernekee wrote:
> > generic-chip.c already has a fair amount of indirection, with pointers
> > to saved masks, user-specified register offsets, and such. Is there a
> > concern that introducing, say, a pair of readl/writel function
> > pointers, would cause an unacceptable performance drop?
>
> I don't know. Thomas' reply suggests that it isn't. Doing byteswap
> in software at a register access is usually free in terms of CPU
> cycles, but an indirect function call can be noticeable if we do
> that a lot.
I did not say that it is free. I merily said that I prefer to have
this solved at the core level rather than at the driver level. So you
have several options to do so:
1) Indirections
2) Different functions for the different access modes
3) Alternatives
#1 Is the simplest solution, but imposes the overhead of an indirect
function call for something trivial
#2 The most efficient and flexible way if you have to provide
different access modes for different drivers. But it comes with the
price of increasing the text foot print.
#3 Smart and efficient, but requires that on a particular system all
drivers use the same access mode.
Thanks,
tglx
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