[PATCH RFC v2 0/3] Add support for Hisilicon SMMU architecture

[Will Deacon]

On Tue, Jun 17, 2014 at 07:32:47AM +0100, leizhen wrote:
> On 2014/6/17 0:37, Will Deacon wrote:
> > On Thu, Jun 12, 2014 at 06:08:09AM +0100, Zhen Lei wrote:
> >> Changes in v2:
> >>
> >> - Split Hisilicon smmu implementation in a separate file, hisi-smmu.c
> >> - Refactor arm-smmu.c. Some direct call hardware dependent functions replaced
> >>   with hooks. And move common struct and marco definition into arm-smmu.h
> >> - Merge the description of Hisilicon private properties into arm,smmu.txt
> >>
> >> Hisilicon smmu is similar to arm-smmu, some code can be direct reused. For
> >> example: map and unmap, device tree configuration, and the software framework.
> >> I found that, abstract about 11 hardware dependent functions in arm-smmu.c is
> >> enough . Abstract means use hooks to replace the direct call of functions. Now,
> >> if need to support Hisilicon SMMU or others arm smmu variants, just selective
> >> rewrite these hooks. And I add a dt_cfg_probe hook, to allow each variant parse
> >> their hardware special configuration. Finally, flush_pgtable is a special case,
> >> hardware independent but maybe referenced. So, total 13 hooks.
> > 
> > The fundamental question here is whether or not your SMMU implementation is
> > intended to follow the ARM SMMU architecture specification. Given the
> > changes you've highlighted, it clearly doesn't comply, so then it comes down
> > to how much code can actually be re-used between arm-smmu.c and hisi-smmu.c.
> > 
> > With your current split, I can still see plenty of duplication between the
> > two files (e.g. bits in the SCTLR register). I also recognise a fair number
> > of lines in hisi-smmu.c that I wrote originally.
> > 
> > So, is this supposed to be architecturally compliant with the ARM SMMU spec
> > or is it something completely independent?
> > 
> > Will
> > 
> > .
> > 
> Yeah, it doesn't comply, and finally will not comply too. So, I said before:
> "similar to" and "arm-smmu variant" maybe inappropriate. It looks like a new
> smmu hardware implementation.

Well, apart from the parts that are identical, sure.

> I also want to reuse your code as much as possible. But in order to keep your
> code flow clearly, I try to make as few changes as possible. I think make
> differentiate granule too small is not well. Because all of our codes maybe
> changed in future, and may any other smmu variants to reuse arm-smmu.c.
> 
> Especially, SCTLR register, the hardware dependent feature. I think not
> suitable for reuse. A bit field differentiation may need a marco to seperate,
> make the code ugly.

I disagree. You have a register with a same name, with the same bits, in the
same positions. That's hopefully not just luck, so the code should be shared
between the drivers. I'm not at all happy with simply duplicating what we
have and bodging it for your purposes -- that totally defeats the point of
having an architecture, even if you're not following it entirely.

Will