On Saturday 17 March 2012, Grant Likely wrote: > On Thu, 15 Mar 2012 09:26:52 +0000, Russell King - ARM Linux <linux@xxxxxxxxxxxxxxxx> wrote: > > On Thu, Mar 15, 2012 at 09:22:06AM +0000, Arnd Bergmann wrote: > > > On Thursday 15 March 2012, Nicolas Ferre wrote: > > > > Add some basic helpers to retrieve a DMA controller device_node and the > > > > DMA request specifications. By making DMA controllers register a generic > > > > translation function, we allow the management of any type of DMA requests > > > > specification. > > > > The void * output of an of_dma_xlate() function that will be implemented > > > > by the DMA controller can carry any type of "dma-request" argument. > > > > > > > > The DMA client will search its associated DMA controller in the list and > > > > call the registered of_dam_xlate() function to retrieve the request values. > > > > > > > > One simple xlate function is provided for the "single number" type of > > > > request binding. > > > > > > > > This implementation is independent from dmaengine so it can also be used > > > > by legacy drivers. > > > > > > > > For legacy reason another API will export the DMA request number into a > > > > Linux resource of type IORESOURCE_DMA. > > > > > > This looks very good. I missed the first version of this patch, but was > > > thinking of very similar bindings. > > > > There's one issue which is concerning me - when we switch OMAP to use > > DMA engine, it won't use numeric stuff anymore but the DMA engine way > > of requesting a channel (match function + data). > > > > How does that fit into this scheme? > > Not well as the current patch set stands. The xlate function doesn't return > any context for the dma channel number that it returns, so the driver cannot > figure out which DMA controller to use if there are multiple. Shouldn't that be part of the data returned by xlate? I was under the impression that this would be the data that you would pass into dma_request_channel, together with a filter function that find the instance from the data. That's why I suggested adding another helper function that would provide a generic filter function for the dt binding doing just that. Arnd -- To unsubscribe from this list: send the line "unsubscribe linux-omap" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
