Cache control

Marco Stornelli marco.stornelli at
Fri Oct 17 18:18:42 EST 2008

Hi Robert,

Robert Woodworth ha scritto:
> I have a Virtex4 VF60 device with 256MB DDR2.
> I have told the Linux kernel that the device has only 128MB and its
> working fine. 

How? Have you used the mem kernel option?

 There is an HDL module that is populating the next 16MB
> with sensor data (0x08000000 - 0x09000000)  I mapped the area into my
> driver via `ioremap()` and also via `mmap / remap_pfn_range()`  It works
> fine.
> I know that PPC cache regions work in 128MB blocks.  I assume that the
> kernel bootup is turning on cache in the first 128, because it thinks
> that its the full RAM range, and not cached in the next 128MB.
> I know that if I declare the area cached, and invalidate the region
> before I read it,  the reads should be much faster than if it's not cached.
> How can I control if the area is cached? and then invalidate it when new
> data arrives?

If you use the ioremap, it provides non-cacheable guarded mappings,
indeed it calls __ioremap with _PAGE_NO_CACHE and _PAGE_GUARDED flags.
You can try to call directly __ioremap with the proper flags.

> Is there a PPC/Linux API call to declare the region cached and
> invalidate regions before read?

Yes, of course. You can see the arch/powerpc/include/asm/cacheflush.h
file to view the API to manage the cache.

> Rob.
> _______________________________________________
> Linuxppc-embedded mailing list
> Linuxppc-embedded at


Marco Stornelli
Embedded Software Engineer
CoRiTeL - Consorzio di Ricerca sulle Telecomunicazioni

marco.stornelli at
+39 06 72582838

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