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Date:   Wed, 26 Dec 2018 08:52:48 -0800 (PST)
Subject:     Re: [PATCH] RISC-V: defconfig: Enable Generic PCIE by default
In-Reply-To: <alpine.DEB.2.21.9999.1812211124180.777@viisi.sifive.com>
CC:     Alistair Francis <Alistair.Francis@wdc.com>,
        Paul Walmsley <paul.walmsley@sifive.com>,
        linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org
From:   Palmer Dabbelt <palmer@sifive.com>
To:     Paul Walmsley <paul.walmsley@sifive.com>
Message-ID: <mhng-ceba7c1a-7334-4869-a7d4-2326b59f82b5@palmer-si-x1c4>
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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.