On 29/09/15 16:34, Arnd Bergmann wrote: > On Tuesday 29 September 2015 15:18:07 Jon Hunter wrote: >> On 29/09/15 13:39, Arnd Bergmann wrote: >>> 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? >> >> I don't think that that would be necessary. If you look at the existing >> tegra i2s binding [0], there is a ahub-cif-ids property which maps the >> actual slave to the apbif (equivalent of the adma-if). This ID is used >> to get the appropriate dma channel for this client interface (cif). >> >>> * How do you model the xbar in this scenario? >> >> The xbar is common to existing tegra devices and today is configured via >> the ahub-cif-ids property. > > I see, so instead of modeling the xbar as part of the DMA engine in DT, you > model it as part of the slave. This probably adds a bit of complexity > and a somewhat nonstandard binding, but it's too late to change that anyway. > >>> * 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). >> >> The channels can be configured to be either rx or tx and yes the IDs do >> overlap so you have 1-10 for both rx and tx. However, if you are asking >> how do I ensure that only one channel uses a specific hardware request, >> then yes I probably need to add the direction to the specifier to ensure >> only one channel uses a request at any given time. > > If each channel is either rx or tx, but the two cannot be used simultaneously, > you can just list each of them only once, like this: > > dmas = <&adma 0>, <&adma 1>, <&adma 2>, ... > dma-names = "if0", "if1", "if2", ... > > Otherwise you end up allocating twice the number of channels that you > really need. Each dma channel can be configured for either tx or rx. There are 10 tx ports on the adma-if and 10 rx. So you could have 20 dma channels configured for each one of the tx and rx ports. It is a bit confusing because rx port 1 has a request signal of 1 and tx port 1 has a request signal of 1 as well. So if you are wondering how the dma distinguishes between rx port 1 and tx port 1, it does so by having a separate field for the tx and rx request in the dma channel control register. Cheers Jon -- 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
