Re: DeviceTree FPGA bitstream

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Hi Walter,

On Thu, Jun 11, 2015 at 12:17:05PM +0200, Walter Goossens wrote:
On 06/09/2015 04:49 PM, Federico Vaga wrote:
- it looks like the DeviceTree is disable for x86 architecture except for
some specific platform. Is it possible to enable it for the entire x86
architecture? Are there any reason to disable it by default?

- I read that since versione 3.17 it should be possible to dynamically
add
portion of DeviceTree from configfs. Is it possible on all architecture?

- I'm working on x86_64 and my FPGA can be on a pluggable board (e.g.
PCIe).
Is there a way to describe this situation with DeviceTree? Is there
any tool
that dynamically computes the addresses (interrupts) translation to use
(e.g. on PCIe) ?


I've been using this scheme on PPC for quite some time (before
devicetree overlays) by creating a custom pcie driver (that knows the
bar addresses and irqs) which then instantiates a "virtual platformbus"
at the pcie bar the fpga is located in.
You can adopt this scheme for x86 by creating a bus and using the
devicetree code to probe the inside of your FPGA but this is all a bit
hackish.
The correct approach (in my opinion) would be to use an overlay
describing the contents of the FPGA and loading that when probing the
pcie-device.

This is more or less what I thought

This would however require a base devicetree to apply the
overlay to, and I'm not sure how much effort this is going to be on x86_64

Not sure but I fear that is not enough to make it stable. The compilation of
the DeviceTree is allowed only on x86 and on some specific platform.

Of course, I can modify the Kconfig to allow the compilation of the
DeviceTree but then I don't know if it will work and how it will work.
I mean are there particular reasons to keep the DeviceTree away from x86 ?
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