On Sat, May 1, 2010 at 4:04 PM, Linus Walleij <linus.ml.walleij@xxxxxxxxx> wrote: > 2010/5/2 Russell King - ARM Linux <linux@xxxxxxxxxxxxxxxx>: > >> Versatile has some MUXing on three of the DMA signals, so (eg) we >> really don't want UARTs claiming DMAs just because they're in existence >> and not in use - that would prevent DMAs from being used for (eg) AACI >> or MMC. > > As long as Versatile doesn't specify any filter function or > data for the channel allocation function (it currently doesn't and defaults > to NULL) it won't even try to call the DMA engine to allocate a channel > for say the UART. > > There is nothing blocking some other peripheral from grabbing a > muxed channel in that case. > > But the implementation of the DMA engine would be better of > handling the muxing dynamically I believe, so when the PL011 > driver (say) requests a DMA channel, it doesn't mean it requests the > *physical* channel and holds it (unless the driver is very naďvely > implemented) it nominally means it reserves a placeholder in the > DMA engine. > > When the driver issues a request to perform a DMA transfer, it will pull > out a physical channel and use that, then return it. If there is too > much combat about the physical channels, you configure out DMA > for the least wanted PrimeCells. > Could you simulate this by publishing more struct dma_chans than are physically present, and then handle the muxing internal to the driver? Or am I misunderstanding the usage model? -- To unsubscribe from this list: send the line "unsubscribe linux-mmc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
