[more info - please help!] MPC7455 DMA buffer strangeness

Paul Mackerras paulus at samba.org
Tue Jul 6 09:44:40 EST 2004

Oliver Korpilla writes:

> I checked my Page Table Entries (PTEs) for the MPC7455 and MPC8240 after the
> remap_page_range() took place.
> Except for the RPN part (the physical address of the page) the PTEs match,
> ending with the last 11 Bits (flags as in arch/ppc/mm/pgtable.h):
> Kernel space: 0x581
> User   space: 0x72D
> (for user space this does mean - from least significant to most significant:
> Page present: 	no,
> Hashed PTE: 	yes,

No, you have _PAGE_PRESENT set and _PAGE_HASHPTE clear there (which
looks correct).

> How are these Linux PTEs mapped to the MMU PTEs (64 bit wide descriptors)?
> The "Programming Environments Manual For 32-Bit Implementations of the PowerPC
> Architecture", the MPC603e and MPC7450 reference manuals depict a completely
> different format, so how and where are these converted? (Hopefully not in
> assembler! ;) )

Yes, in assembler. :)  For the 74xx, it's done by create_hpte() in
arch/ppc/mm/hashtables.S, and for the 603 (and the 8240) it's done by
DataLoadTLBMiss or DataStoreTLBMiss in arch/ppc/kernel/head.S.


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