Håvard Skinnemoen wrote: > Hi, > > On Tue, Sep 27, 2011 at 5:13 AM, Arvid Brodin <arvid.brodin@xxxxxxxx> wrote: >> [Resending with CC to affected parties] >> >> Hi, >> >> I would expect cache synchronization for DMA_TO_DEVICE and DMA_BIDIRECTIONAL >> when dma_map_single() is called, and for DMA_FROM_DEVICE and DMA_BIDIRECTIONAL >> when dma_unmap_single() is called. >> >> However, on some architechtures (at least avr32, blackfin, ...), cache >> synchronization only happens when dma_map_single() is called (and then >> irrespective of DMA direction). dma_unmap_single() is a no-op for these archs. >> >> See e.g. http://lxr.linux.no/#linux+v3.0.4/arch/avr32/include/asm/dma-mapping.h#L117 >> >> Isn't this a bug? > > I don't think so. What do other architectures do? > > We always need to sync before the transfer because if there is dirty > data in the cache, it might get written to RAM during the transfer, > which would be bad. Then, since the relevant cache lines are already > clean and invalid, and the CPU is not allowed to access the buffer > during the transfer, there's no need to sync again when the transfer > is complete. I see. Thanks for the explanation! > > Havard -- Arvid Brodin Enea Services Stockholm AB -- To unsubscribe from this list: send the line "unsubscribe linux-embedded" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
