ppc440 caches - change proposal [RFC]

John Bonesio john.bonesio at xilinx.com
Thu Apr 10 04:00:40 EST 2008

Hi Grant,

I have a question about your patch. It appears as if the cache setup code is in a file that would be used only on Xilinx FPGA devices.

I understand that many people are using a bootloader that already sets up the cache for the kernel, but I'm wondering if Xilinx boards are really a special case, or if there may be other non-Xilinx related systems that would also not be using a bootloader.

I also understand the desire to avoid code that does the same work more than once, but I wonder if in this case, it's creating too strong a dependence on the specific behavior of a certain bootloader.
I also wonder if arch/powerpc is being made more complex by trying to split out this code change into a Xilinx specific area, when the change could just be rolled into head_40x.S and we could do away with virtex405-head.S.

Just some thoughts,

- John

On Tuesday 08 April 2008 16:15, you wrote:
> On Tue, Apr 8, 2008 at 4:56 PM, Benjamin Herrenschmidt
> <benh at kernel.crashing.org> wrote:
> >
> >  On Tue, 2008-04-08 at 15:53 -0700, John Bonesio wrote:
> >  > I was thinking it might be good to have the kernel initialize these
> >  > cache control registers in it's own start up code. Or perhaps this
> >  > could be done in the kernel's simple bootloader. We could probably put
> >  > this change in a Xilinx specific startup file, but this change doesn't
> >  > seem specific to Xilinx FPGA boards.
> >
> >  The kernel's wrapper would be a good place to put that I suspect. That's
> >  the kind of thing that should be provided as a "library" function to be
> >  optionally called by platform code. Either in the wrapper or the main
> >  kernel platform code.
> Code is already queued up for 2.6.26 to do exactly this on ppc405
> virtex platforms.  We can do the same thing for 440.  Look at
> virtex405-head.S in the following patch:
> http://patchwork.ozlabs.org/linuxppc/patch?person=486&id=17410
> Cheers,
> g.
> -- 
> Grant Likely, B.Sc., P.Eng.
> Secret Lab Technologies Ltd.

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