On Tuesday 29 September 2015 13:18:06 Jon Hunter wrote: > > On 28/09/15 16:07, Arnd Bergmann wrote: > > On Monday 28 September 2015 15:57:46 Jon Hunter wrote: > > [snip] > > >> Actually, what I mentioned about would not work as it is not the DMA > >> that should assign the requests to the channel. > >> > >> I think that I have poorly described the hardware and how it works, so > >> let me try and explain a bit more. > >> > >> From a hardware perspective it looks like the following ... > >> > >> memory <-> adma <-> adma-if <-> xbar <-> clients > >> > >> where: > >> - memory is the system memory > >> - adma is the dma controller > >> - adma-if is the dma interface to a crossbar > >> - xbar is the crossbar > >> - clients are various audio interfaces, such as i2s, etc > >> > >> The adma-if is essentially a mux with 10 tx and 10 rx ports. Any of the > >> 22 adma channels can be mapped to any of the 10 tx or rx ports. The > >> request signal used by the adma is determined by which port it is > >> configured to use. However, what makes this even more configurable is > >> the xbar is also a mux that can route adma-if ports to the various clients. > >> > >> So potentially, you could use any adma channel and any port to route > >> audio to any of the clients. However, the adma-if needs to know which > >> adma channel is mapped to which port and so it probably makes most sense > >> for the adma-if binding (not in the mainline yet) so specify a mapping > >> even though any mapping could be used. > >> > >> admaif@0x702d0000 { > >> dmas = <&adma 1>, <&adma 1>, <&adma 2>, <&adma 2>, > >> ... > >> dma-names = "rx1", "tx1", "rx2", "tx2", > >> ... > >> }; > >> > >> Alternatively, I was thinking that I could set #dma-cells = 0, but what > >> I should have done is just have something like ... > >> > >> admaif@0x702d0000 { > >> dmas = <&adma>, <&adma>, <&adma>, <&adma>, > >> ... > >> dma-names = "rx1", "tx1", "rx2", "tx2", > >> ... > >> }; > >> > >> In the above case the adma-if driver can just pick whatever channel it > >> wants for each of the ports. > >> > >> Hope this is clearer. > > > > I think what you are saying here is that the ADMA driver does not talk > > to dma slave devices at all, but only talks to the adma-if, which in > > turn only talks to the xbar. > > Yes, this is the use-case that this current version of the driver > supports. However ... > > > That is fine, but the result of that is that there is no point in > > using the DMA slave binding for this device, or for the driver to > > register itself as a generic slave driver, which it is not. > > ... the DMA controller itself has a source and destination register and > from a hardware perspective, the source and/or destination does not need > to be the ADMA-IF. Potentially, we could support memory to memory > transfers, but currently we are not using the DMA for this. So I can see > that with the current usage it may not make sense for it to be > registered as a generic slave driver, but from a hardware perspective I > think it still does. Ok, but imagine a device where the ADMA is actually wired up to a slave directly. In this case, you need #dma-cells=<1> (or higher) to identify which slave that is. If you want the binding to be generic enough to handle that case, it needs to correctly describe the identification of the request lines. > The current tegra audio drivers use the snd_dmaengine_xxx helpers and so > it would be nice to do the same here. That seems to be a separate (non-)problem, as the audio devices would have their 'dmas' properties pointing to the adma-if or the xbar (depending on how you define those bindings), and don't need to change either way. > > We should look at this driver in combination with the adma-if and > > xbar drivers and then define a binding for the combination of those. > > Yes that makes sense, but I think that I have confused matters here a > bit and not thought through this entirely. So while we could configure > an audio interface, such as i2s, to use any adma-if port and hence any > dma channel with the appropriate hardware request signal, the mapping > between the adma-if port and request signal is fixed. For example, > > adma-if rx1 port uses adma request signal 1 > adma-if rx2 port uses adma request signal 2 > adma-if rx3 port uses adma request signal 3 > ... > adma-if rx10 port uses adma request signal 10 > > and > > adma-if tx1 port uses adma request signal 1 > adma-if tx2 port uses adma request signal 2 > adma-if tx3 port uses adma request signal 3 > ... > adma-if tx10 port uses adma request signal 10 > > What is connected to these adma-if tx and rx ports who knows but I think > that is where I was going wrong and made this more complex than it > should have been. So I think that the adma binding should have > #dma-cells = 1 and the adma-if binding have the following ... > > admaif@0x702d0000 { > dmas = <&adma 1>, <&adma 1>, <&adma 2>, <&adma 2>, > ... > dma-names = "rx1", "tx1", "rx2", "tx2", > ... > }; Ok, that makes more sense then. A few questions still: * Would the admaif in turn provide a #dma-cells and have the real slaves hooked up to it? * How do you model the xbar in this scenario? * How does the adma driver know whether you are using a rx or tx channel in the above example, should that perhaps be another cell in dma specifier? It seems that the numbers are all overlapping between rx and tx (each has 1 through 10). Arnd -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html