Messages in this thread | | | Subject | Re: [PATCH] generic device DMA (dma_pool update) | Date | Tue, 31 Dec 2002 17:47:49 -0600 | From | James Bottomley <> |
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david-b@pacbell.net said: > USB device drivers tend to either allocate and reuse one dma buffer > (kmalloc/kfree usage pattern) or use dma mapping ... so far.
Please be careful with this in drivers. Coherent memory can be phenomenally expensive to obtain on some hardware. Sometimes it has to be implemented by turning off caching and globally flushing the tlb. Thus it really makes sense most of the time for drivers to allocate all the coherent memory they need initially and not have it go through the usual memory allocate/free cycle except under extreme conditions. That's sort really what both pci_pool and mempool aim for.
James
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