Disable cache on 74xx

[Geert Uytterhoeven]

On 20 Feb 2003, Gary Thomas wrote:
> On Thu, 2003-02-20 at 06:55, Brian Waite wrote:
> > According to The User's Manual, the data cache instructions become no-ops if
> > the data cache is disabled.
>
> There are "User Manuals" and then there is "Real Life".  My
> experience has been that trying to execute these instructions
> with the cache disabled was treated like an invalid instruction
> (hence causing a trap).  Maybe this isn't always true with all
> PowerPC processors, but I was just pointing out that you might
> run into trouble with it.

There may be a different behavior for `disabling the data cache globally' and
`using e.g. dcbf on uncached memory' (with the data cache enabled globally).

> > On Wednesday 19 February 2003 5:48 pm, Gary Thomas wrote:
> > > On Wed, 2003-02-19 at 14:07, Benjamin Herrenschmidt wrote:
> > > > On Wed, 2003-02-19 at 21:52, Brian Waite wrote:
> > > > > Hi all,
> > > > > 	I am trying to hunt down a memory controller configuration problem and
> > > > > I have been asked to disable all caching so as to remove it from the
> > > > > equation. I can easl disable L2 but when I start ucking with the WIMG
> > > > > bits to set cache inhibit, The kernel panics with stack overflows. Does
> > > > > anyone know where or what I have to set to disable caching?
> > > >
> > > > Hrm... set L2 and L3 off, then hack HID0 to disable L1 ?
> > >
> > > There are other problems with this.  With the caches disabled
> > > (via HID0) all data cache instructions (like DCBF) will fail.
> > > There are some of these in the kernel itself, but beware that
> > > GLIBC has it's own set.
> > >
> > > ... totally disabling the data CACHE with Linux is non-trivial.

Gr{oetje,eeting}s,

						Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert at linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
							    -- Linus Torvalds


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