Messages in this thread | | | Date | Fri, 18 Jan 2002 13:02:09 -0600 | From | Troy Benjegerdes <> | Subject | pci_alloc_consistent from interrupt == BAD |
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Somehow the docs in DMA-mappings.txt say pci_alloc_consistent is allowed from interrupt, but this is a "bad thing" on at least arm and PPC non-cache coherent cpus.
On these cpus we have to allocate page tables for consistent_alloc.. I really dont' think we want to be doing this during interrupt context.
This also causes the sym53c8xx_2 driver to not work on some embedded ppc 4xx boards, and in general, seems to be a 'bad thing' to allow.
For example, in the arch/arm/consistent.c:
/* * This allocates one page of cache-coherent memory space and returns * both the virtual and a "dma" address to that space. It is not clear * whether this could be called from an interrupt context or not. For * now, we expressly forbid it, especially as some of the stuff we do * here is not interrupt context safe. * * Note that this does *not* zero the allocated area! */ void *consistent_alloc(int gfp, size_t size, dma_addr_t *dma_handle)
(arm's pci_alloc_consistent always calls consistent_alloc).
The PPC version calls a similiar function when CONFIG_NOT_COHERENT_CACHE is defined. On 'regular' ppc machines, it's just a __get_free_pages, which is why no one from the pmac crowd has screamed.
-- Troy Benjegerdes | master of mispeeling | 'da hozer' | hozer@drgw.net -----"If this message isn't misspelled, I didn't write it" -- Me ----- "Why do musicians compose symphonies and poets write poems? They do it because life wouldn't have any meaning for them if they didn't. That's why I draw cartoons. It's my life." -- Charles Schulz - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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