On Jan 30, 2008 1:56 AM, Haavard Skinnemoen <[EMAIL PROTECTED]> wrote: > On Tue, 29 Jan 2008 22:56:14 -0800 > David Brownell <[EMAIL PROTECTED]> wrote: > > > On Tuesday 29 January 2008, Haavard Skinnemoen wrote: > > > > > > Btw, there's one issue I forgot to mention: I believe the DMA Engine > > > framework is currently misusing the DMA mapping API, and this patchset > > > makes things worse. > > > > > > Currently, the async_tx bits of the API do the required calls to > > > dma_map_single() and/or dma_map_page(), but they rely on the driver to > > > do the unmapping. This is problematic ... > > > > > > How do we solve this? > > > > How about: for peripheral DMA, don't let the engine see anything > > except dma_addr_t values. > > I don't think it does, but the dma_addr_t value is enough to call > dma_unmap_single() and dma_unmap_page().
Right, dma_addr_t values are all the driver sees in the current scheme. > > > The engine needs to be able to dma_alloc_coherent() memory too, > > which is pre-mapped. > > Right, which is another argument for not doing any unmapping in the DMA > engine driver. We really need to push this responsibility to the client. > Agreed, the issue is how to do this without requiring an interrupt+callback sequence for each transaction or requiring the client to carry per transaction unmap-data. For example NET_DMA never sees a dma_addr_t and assumes that all it needs to care about is the last transaction in a sequence. Since it is alive for the duration of a transaction, we could put unmap data in dma_async_tx_descriptor along with an unmap function pointer since dma_unmap* routines have an equal number of parameters. But I just got through making this structure smaller so maybe there is a better way. -- Dan -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
