On 6 July 2018 at 03:15, Paul Cercueil <paul@xxxxxxxxxxxxxxx> wrote: > > >> Paul, >> >> On 3 July 2018 at 18:02, Paul Cercueil <paul@xxxxxxxxxxxxxxx> wrote: >>> >>> The register area of the JZ4780 DMA core can be split into different >>> sections for different purposes: >>> >>> * one set of registers is used to perform actions at the DMA core level, >>> that will generally affect all channels; >>> >>> * one set of registers per DMA channel, to perform actions at the DMA >>> channel level, that will only affect the channel in question. >>> >>> The problem rises when trying to support new versions of the JZ47xx >>> Ingenic SoC. For instance, the JZ4770 has two DMA cores, each one >>> with six DMA channels, and the register sets are interleaved: >>> <DMA0 chan regs> <DMA1 chan regs> <DMA0 ctrl regs> <DMA1 ctrl regs> >>> >>> By using one memory resource for the channel-specific registers and >>> one memory resource for the core-specific registers, we can support >>> the JZ4770, by initializing the driver once per DMA core with different >>> addresses. >> >> >> As per my understanding device tree should be modified only when >> hardware changes. This looks the other way around. It must be possible >> to achieve what you are trying to do in this patch without changing >> the device tree. > > > I would agree that devicetree has an ABI that we shouldn't break if > possible. > > However DTS support for all the Ingenic SoCs/boards is far from being > complete, and more importantly, all Ingenic-based boards compile the DTS > file within the kernel; so breaking the ABI is not (yet) a problem, and > we should push the big changes right now while it's still possible. Completely agree with you in this. Let's wait and see what DT maintainer's view.
