Re: [PATCH] RISC-V: defconfig: Enable Generic PCIE by default

From: Palmer Dabbelt
Date: Wed Dec 26 2018 - 11:52:54 EST

On Fri, 21 Dec 2018 11:27:39 PST (-0800), Paul Walmsley wrote:

On Fri, 21 Dec 2018, Alistair Francis wrote:

When the MicroSemi driver does eventually go upstream this will
probably have to be discussed though as either the config or device
tree will need to be edited to ensure only one PCIe device is present.

The right way to do that is to have two separate DT files: one for the
HiFive-U board alone; the other for the HiFive-U plus the expansion board
combo. There shouldn't be any problems with keeping both drivers enabled
in the defconfig.

We actually need at least three:

* One for the HiFive Unleashed
* One for the HiFive Unleashed, when attached to the Micro Semi expansion board.
* One for the HiFive Unleashed, when attached to a VC707.

We may end up needing additional device trees for the newer Xilinx boards, depending on if it's possible to probe for that 32-bit DMA limit on the VC707 or not. Then, of course, we'll need an image-specific device tree whenever we put an accelerator on the FPGA.

Ideally we'd have a discoverable bus, but that's going to be a bit of a way out. For now we'll have to get by with different device trees, but that should get significantly easier when we get a proper bootloader working.