Re: public git l2 cache off.

Tony Lindgren
2008-05-06T21:25:45Z

* Koen Kooi <k.kooi@student.utwente.nl> [080506 10:02]:
>
> Op 6 mei 2008, om 18:51 heeft Woodruff, Richard het volgende geschreven:
> >> Beagleboard (omap3530)
> >>
> >>> I'll try the latest from here on SDP with this and see if it works.
> >>> There is also a difference in CR handling. I had submitted long
> >>> back a fix to Russell but let it get by me as I didn't have the time
> >>> to fix per his comments. I think our version was more correct then
> >>> the one in place but was still lacking a bit.
> >>>
> >>> [*] It seems possible you could have an issue depending on what your
> >>> boot loader is or isn't doing for you.
> >>
> >> U-boot (both 1.1.4 and 1.3.2) calls l2disable() before booting linux,
> >> so linux needs to enable it. I vote for removing the l2disable() in
> >> u-
> >> boot, but I can see that people might be stuck with broken binary
> >> bootloaders...
> >
> > Yes, this 'might' help for some users if it works. Traditionally
> > things usually have had some complications here at multiple levels
> > in both hardware and software. And yes not everyone can upgrade a
> > boot loader. However, with expanding boot from MMC/SD support
> > things are getting safer.
> >
> > The bit I was more worried about was the boot loader may not be
> > invalidating secure L2 tags correctly. The method to do this
> > correctly is a little different between EMU/HS and GP devices. Also
> > these base methods changed some between ES1 and ES2 of the chip. I
> > hope no one is using an ES1 anymore but I'm sure code remnants exist.
> >
> > The working code variants did some work in u-boot and some in the
> > kernel to handle these conditions. The current balance today in
> > working variants today has u-boot doing more work. This probably
> > merges with fewer conflicts with the arm-kernel. Last I checked u-
> > boot on Beagle was a based on an older version of the code and
> > probably even a wider range of versions exist in the community. As
> > such it's a good bet some of this is at the root of the problems you
> > are seeing.
>
> I'm currently using the u-boot Jason built (1.3.2 + beagle patches)
> which disables l2 cache before boot and I switch between 2.6.22-wtbu
> (which enables L2) and git HEAD (which doesn't enable L2).

Sounds like the bootloader should configure L2 cache and just leave
the C bit off for kernel looking at the "Cortex-A8 L2 cache handling at
startup?" thread on linux-arm-kernel. I guess the L2 configuration
is implementation specific and cannot be read from the ARM registers.

Regards,

Tony

>
> regards,
>
> Koen
>
>
> >
> >
> > It is important to keep x-loader/u-boot/kernel somewhat in sync for
> > some of these kinds of issues until the development process has
> > settled down and code matured.
> >
> > L2 cache is a huge performance boost on an OMAP3 so it's good to get
> > it. Also you really haven't validated your software if you're
> > running with it off.
> >
> > Regards,
> > Richard W.
> >
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