On Mon, Sep 24, 2018 at 03:32:44PM -0500, Alan Tull wrote: > My interest here was in having some discussion on whether connectors > are a good match for handling FPGAs. > > The relevant use model is where a user applies a DT overlay targeting > an FPGA region after the kernel has booted. That overlay initiates > FPGA programming and then adds nodes for the new FPGA hardware. This > is discussed more completely in the FPGA manager DT binding document > [1]. The main deal here is that I'd like to be able to add nodes > in/below a FPGA region node to support devices in the FPGA (and be > able also to remove them if we are going to reconfigure the FPGA.) > > Previous discussions about DT connectors focused on the types of > things likely to be on a physical connector. GPIO and SPI got named as > good examples for discussion while MMIO specifically was dismissed > [2]. That's problematic for embedded FPGAs for example since the FPGA > is on a mmio bus and hardware that is programmed into the FPGA lives > on that mmio bus similar to any embedded peripherals. So there's a > question - are mmio busses intended to be left un-connectorizable? I don't see any particular reason that a connector couldn't be used for mmio devices. I think you'd want to treat the connection point as a bridge on the mmio bus - that can have a 'ranges' property mapping the connected device into the parent bus's address space (as an identity mapping or otherwise). > > Alan > > [1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/devicetree/bindings/fpga/fpga-region.txt > > [2] https://lkml.org/lkml/2016/7/20/560 > -- David Gibson | I'll have my music baroque, and my code david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_ | _way_ _around_! http://www.ozlabs.org/~dgibson
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