Messages in this thread |  | | | Subject | Re: [PATCH 2/3] define ARM-specific dma_coherent_write_sync | | From | Mark Salter <> | | Date | Tue, 06 Sep 2011 10:37:15 -0400 |
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On Tue, 2011-09-06 at 15:32 +0100, Catalin Marinas wrote: > That's what mb() and wmb() do already, at least on ARM. Why do we need > another API? IIRC from past discussions on linux-arch around barriers, > the mb() should be sufficient in the case of DMA coherent buffers. > That's why macros like writel() on ARM have the mb() added by default > (for cases where you start the DMA transfer by writing to a device > register).
For USB EHCI, the driver does not necessarily write to a register after writing to DMA coherent memory. In some cases, the controller polls for information written by the driver.
--Mark
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