Re: [Qemu-devel] [Qemu-ppc] [0/8] RFC: target-ppc: Start disentangling different MMU types

[David Gibson]

On Fri, Feb 22, 2013 at 05:15:22PM +0100, Alexander Graf wrote:
> 
> On 12.02.2013, at 03:00, David Gibson wrote:
> 
> > The target-ppc code supports CPUs with a number of different MMU
> > types: there's both the 32-bit and 64-bit versions of the "classic"
> > hash page table based powerpc mmu and there's also the BookE and 40x
> > MMUs.
> > 
> > Currently handling of all these has a roughly shared path in
> > mmu_helper.c.  Although code sharing is usually a good idea, in this
> > case the MMUs really aren't similar enough for this to be useful.
> > Instead it results in checking and behaving differently at many, many
> > different points in the path leading to an unreadable tangle of code.
> > 
> > This patch series is a first step to cleaning this up, moving to a
> > model where we have a single switch on the MMU family at the top-level
> > entry points, then have a simpler, clearer separate code path for each
> > MMU type.  More specifically, it disentangles the path for the 64-bit
> > classic hash MMU into its own new file.  The other MMU types keep the
> > existing code (minus 64-bit hash specific conditionals) for now.
> > Disentangling those as well would be a good idea, but would be best
> > done by someone with more resources to test those other platforms than
> > I have.
> > 
> > For now, the resulting 64-bit hash path retains the same structure as
> > the original shared code, just the obvious conditionals on other mmu
> > types are removed.  This path is fairly ugly in itself, but cleaning
> > that up is a later step, now much simpler without the other MMU types
> > to deal with at the same time.
> 
> Looks like a nice and long overdue cleanup. A few points I'd like to see 
> addressed:
> 
>   - Instead of exporting common helper functions, put them into a
>   new mmu-hash.h as static inline. That way things can get optimized
>   a lot better.

The common helpers are all gone again by the end of the series, so is
there really any point?

>   - Please extract the 32bit hash functions into a separate file as
>   - well. You're touching all that code anyways, so I'm sure you can
>   - test it :). 

Sigh.  If I must.

>   - QOM'ify things please :). Just make your mmu type specific
>   - function calls function pointers in the class and invoke them
>   - from there instead of the switchery.

Ok.  I think that works best as an extension to the series, rather
than actually changing any of the existing patches.

-- 
David Gibson                    | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au  | minimalist, thank you.  NOT _the_ _other_
                                | _way_ _around_!
http://www.ozlabs.org/~dgibson

signature.asc
Description: Digital signature