Hi Vinod, On 07/20/2012 04:37 AM, Vinod Koul wrote: > On Fri, 2012-07-20 at 08:39 +0000, Arnd Bergmann wrote: >> On Friday 20 July 2012, Vinod Koul wrote: >>>> Required property: >>>> dmas: list of one or more dma specifiers, each consisting of >>>> - phandle pointing to dma controller node >>>> - flags word, a bit map that can hold these flags >>>> * 0x00000001 channel can be used for transfer from device >>>> * 0x00000002 channel can be user for transfer to device >>> >>> Is this for identifying which channel is for TX and RX? If not I am not >>> sure I understood it well >> >> Yes, but we can potentially add more flags here. >> >> The argument we had when coming up with this was roughly: >> >> * we need to identify which specifiers are referring to the same >> conceptual channel and can be used as alternatives >> * this could be done just using the dma-names property, but making >> dma-names mandatory adds complexity for everyone. >> * Most devices have just one or two channels, and if they have two, >> there is usually one input and one output. >> >> => if the common dmaengine code can find out whether a channel is >> input or output without looking at the dmac driver specific configuration, >> we don't need to add dma-names in most cases, but just let the client >> driver ask for "give me a channel with these flags". > No we don't export the direction of the channel and usually channel can > be configured either way.
So yes I can see that a channel itself could be configured to support a given direction, but when we ask for a channel via dma_request_channel() we are going to get a channel that matches the criteria we pass using the filter parameter. So here the thinking was that "flags" is a filter parameter that the user could specify and one example being direction but it could be something else too. > But from a client POV it makes sense as with the given direction you > would need a specific request line for a channel. So this is right. > But direction is something I don't expect to be used for "give me a > channel" Ok. The thought was that the user would have the following means of requesting a channel ... 1. By name 2. By a filter parameter (flags) 3. By name and a filter parameter So we would have the following APIs ... struct dma_chan *of_dma_request_channel(struct device_node *node, unsigned int flags); struct dma_chan *of_dma_request_named channel(struct device_node *node, char *name, unsigned int flags); In both of these the filter parameter flags is optional. Let me know your thoughts on this. Cheers Jon _______________________________________________ devicetree-discuss mailing list devicetree-discuss@lists.ozlabs.org https://lists.ozlabs.org/listinfo/devicetree-discuss
