Messages in this thread | | | Subject | Re: how does one disable processor cache on memory allocated with get_free_pages? | From | Benjamin Herrenschmidt <> | Date | Fri, 27 Feb 2004 21:51:33 +1100 |
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On Fri, 2004-02-27 at 03:25, Ross Tyler wrote: > Andrew, > > Thank you for taking the time to reply. I really appreciate your help. > > My understanding of ioremap_nocache is that it falls short of what I > need to do. > It is appropriate for, say, mapping physical memory on a PCI device that > is marked prefetchable (and otherwise subject to caching when mapped > with ioremap) as non-caching. > Can you confirm my understanding?
No, ioremap always maps non-cacheable, this has nothing to do with the prefetching attribute
> If so, it will not work for me as I am not mapping physical memory but > memory allocated by get_free_pages. > Do you concur?
get_free_pages() returns you physical memory...
> AFAIK, the only way to access this memory without using processor cache > is to have a device driver memory map it for a process like > drivers/char/mem.c does. > When the memory is accessed through these memory mapped pages, the > access will not be cached. > When the memory is accessed through the get_free_pages pages, the access > will be cached. > Concur?
get_free_page allocates cacheable physical memory, nothing to do with your PCI device... ioremap maps your device non-cacheable into the kernel address space.
> In order to access this process mapped memory from outside the context > of the process it was mapped for, one either needs to independently > remap it for the current process (what to do in interrupt code?) or set > up a kiobuf to the memory. > It has been my experience, however, that the pages referenced by the > kiobuf are the same pages returned by get_free_pages. > I expect these same pages have the same (caching) attributes associated > with them which would not work.
What are you trying to do exactly ?
Ben.
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