On Mon, 2012-01-30 at 10:34 +0100, Guennadi Liakhovetski wrote: > > I don't still comprehend the need for a library on top of dmaengine > > which gain is just a library between clients and dmacs. Surely we don't > > want to write another abstraction on top of one provided? > > > > If the question is to handle scatter-gather even if the hardware doesn't > > have the capability, then why don't add that in dmaengine itself rather > > than one more layer? > > Well, yes, adding new abstraction layers is always a decision, that has to > be well justified. In this case it does at least make the life easier for > two sh-mobile drivers: shdma and the new SUDMAC driver. > > However, I did name the library in a generic way without reference to sh, > assuming, that it might with time become useful for other architectures > too. The reasons why I prefered to keep it as an optional addition to > dmaengine core, instead of tightly integrating it with it are, that (1) I > did not want to add useless code to drivers, that do not need it, So are we sure that only sh-mobile drivers need this capablity? Btw does you hardware only support single transfers and no sg support, would this remain the same in future? > (2) I am > not sure if and when this library will become useful for other drivers: > apart from sh I am only familiar with one more dmaengine driver: > ipu/ipu_idmac.c, and that one supports scatter-gather lists in a limited > way and has some further peculiarities, that would likely make it a bad > match for the simple DMA library, typically the dmacs will support this in some form or other, so your point is valid :) > (3) keeping it separate makes its > further development easier. > > OTOH, I'm certainly fine with a tighter library integration with the > dmaengine core. I think, it still would be better to keep it in a separate > file and only build it if needed, right? This woult also simplify code > debugging and further development. I can remove the "simple" notation, > which does make it look like an additional abstraction layer, and replace > it with, say, sgsoft (scatter-gather software implementation)? that would be more apt :) > A more > interesting question is what to do with struct dma_simple_dev, struct > dma_simple_chan, struct dma_simple_desc, that embed struct dma_device, > struct dma_chan and struct dma_async_tx_descriptor respectively. I don't > think we want to merge all the additions from those wrapping structs back > into their dmaengine counterparts? Sure they should be kept separate. I like the wrapping, this keeps it simple. > > How would you like to do this? Don't you think, it would be good to allow > both: either implement a dmaengine driver directly, exactly as all drivers > are doing now, or use the additional helper library for suitable (simple) > hardware types? I see it similar to I2C, where you either implement an I2C > driver directly, or you use the bitbanging abstraction for simpler > hardware. I think it would be good to have both, this can be used by folks who don't have sg support available. -- ~Vinod -- To unsubscribe from this list: send the line "unsubscribe linux-mmc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
