On 11/23/2011 03:25 PM, Stephen Warren wrote: > Rob, Grant, > > Re: http://www.spinics.net/lists/arm-kernel/msg148899.html > > Background: Tegra's DMA controller needs to be told which DMA "request > select" to use for each transfer. The identifies which peripheral to > transfer to/from. > > The Tegra I2S driver needs to know its own "request select" value to > pass to the audio driver DMA path. The board files typically provide > this to the driver as an IORESOURCE_DMA. I don't think there's any > standard binding that creates such a resource when instantiating a > platform device from device tree, and the discussions I found when > looking for one didn't seem to reach conclusion that there should be > one. So, I proposed the following property in the I2S driver's DT > binding for this: I think this is a case of every platform being different and IORESOURCE_DMA is not too widely used. Even on PPC, there's not a standard way. > > Doc: > > - dma-channel : The Tegra DMA controller's channel ID for this I2S controller > > Example: > > i2s@70002800 { > compatible = "nvidia,tegra20-i2s"; > reg = <0x70002800 0x200>; > interrupts = < 45 >; > dma-channel = < 2 >; > }; > > Does that look reasonable? Or, should I pursue some more standardized > solution? I had some discussion with Thomas Abraham about this for the pl330 dma: http://lists.ozlabs.org/pipermail/devicetree-discuss/2011-September/008269.html So I would just add a phandle to the dma controller here. > > (although perhaps dma-request-select would be a better name, since each > of the DMA controller's 16 channels can be used for any of the DMA > selects) You'll find h/w with all sorts of relationships between requests and channels on DMA controller h/w... > > For reference, the code turns out as below; it might be nicer if the > DT parsing code could create this resource for us, although there was > some previous discussion about IORESOURCE_DMA not being the correct > representation for this anyway. > > dmareq = platform_get_resource(pdev, IORESOURCE_DMA, 0); > if (!dmareq) { > if (of_property_read_u32(pdev->dev.of_node, > "nvidia,dma-channel", > &dma_ch) < 0) { It would, but I think IORESOURCE_DMA is supposed to be for ISA bus DMA. Also, I think often you need more information than just a request line like a mode or type of transfer or burst length parameters. Rob -- To unsubscribe from this list: send the line "unsubscribe linux-tegra" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
