On 07/31/2014 09:44 AM, Maxime Ripard wrote: [...]
- Having to set device_slave_caps or not?
Yes. This should in my opinion be mandatory for new drivers. One of the issues with the DMAengine API is that it is really hard to write generic drivers that do not already know about the capabilities of the DMA controller. E.g. if you have a peripheral that is used on SoC A it assumes that the DMA controller it is connected to has the capabilities of the DMA controller in SoC A. If the same peripheral is now used on SoC B with a DMA controller with different capabilities this often ends up with ugly ifdefery in the peripheral driver. The peripheral driver shouldn't have to know which specific DMA controller it is connected to (It's a bit as if a GPIO consumer needed to know which GPIO controller is connected to). We got away with the current approach since there is not that much diversity in the mixing of peripherals and DMA controllers (each vendor pretty has their own DMA controller which it uses for their own peripherals). But with more recent code consolidation we are on a path to generic DMA support within subsystem frameworks (there is generic DMA support for audio, there is generic DMA support for SPI and I also have a (currently) out of tree patch for generic DMA support for IIO). Also these generic drivers need to be able to discover the capabilities of the DMA controller to be able to make the right decisions.
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