Hi Alex, On 26/02/15 20:04, Alex Smith wrote: > Hi Zubair, > > On 26 February 2015 at 12:43, Zubair Lutfullah Kakakhel > <Zubair.Kakakhel@xxxxxxxxxx> wrote: >> From: Alex Smith <alex.smith@xxxxxxxxxx> >> >> Add device tree bindings for the DMA controller on JZ4780 SoCs, used by >> the dma-jz4780 driver. >> >> Signed-off-by: Alex Smith <alex.smith@xxxxxxxxxx> >> Signed-off-by: Zubair Lutfullah Kakakhel <Zubair.Kakakhel@xxxxxxxxxx> >> >> --- >> V3 -> V2 >> Changed binding. >> Used to be 3 DMA cells required. <&dma TX_type RX_type Reserved> >> Now 2 DMA cells are required. <&dma Transfer_type Reserved> >> >> This is more common in DMA bindings. >> And I couldn't figure any reason that 3 cells were used. > > There are different request type numbers for transfers to/from the > same device (see the JZ4780 programmers manual, page 505). While only > having the option to specify one transfer type is OK when the driver > is using separate channels for read/writes, I recall seeing/writing > some other drivers which use a single channel for both reads and > writes. This would not be possible if we can only specify one transfer > type, you'd have to have them separate. > I know. I looked at the drivers and did this on purpose. We'd like to keep the same bindings/code for jz4740/jz4780 peripheral drivers and dma code. Our jz47xx-mmc driver we had was the main culprit I found. As well as the jz4740-i2s one. However, jz4740-mmc upstream driver has improved already for dma and takes two dma channels. And the jz4740-i2s also takes two channels. One for Tx and one for Rx. If we move to 3 cells for jz4780-dma. Then 'ideally' jz4740-dma would need 3 cells too. Or we'd have a binding nightmare everywhere. But when we use jz4740-mmc and jz4740-i2s, we still have to change the driver to share one channel or simply pass them <&dma Tx 0 Reserved> <&dma 0 Rx Reserved> Which makes the binding redundant. There isn't any particular reason a driver would need to share one channel only. The 'special' nand/nemc channels don't have a request type. Thanks, ZubairLK > Thanks, > Alex -- 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
