* RFC: Start-time Device Addition for BMC devices
@ 2020-12-28 20:26 Patrick Venture
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From: Patrick Venture @ 2020-12-28 20:26 UTC (permalink / raw)
To: qemu-devel, Havard Skinnemoen, Hao Wu
Hi;
Currently, devices for a BMC are specified in the board init method
for that machine, see:
- https://github.com/qemu/qemu/blob/b785d25e91718a660546a6550f64b3c543af7754/hw/arm/aspeed.c#L414
This requires listing all i2c devices, and setting some properties.
QMP can be used to set the properties for those devices at run-time
already.
We're looking at developing many BMC boards, but for most boards, the
i2c devices that correspond to PCIe devices vary by configuration --
which PCI cards are plugged into which slots. We'd like to not
hard-code those i2c devices and have variations of the same device
board. For instance:
board-bmc + two cards (slot 1, slot 2)
board-bmc + one card (slot 3)
The slot to i2c bus mapping is beyond the scope of this, because that
isn't something that technically changes*.
To solve this problem, we'd like to add an optional device json
configuration parameter. Using QMP (which I believe supports adding
devices of this type in the schema), the file would be parsed after
the board_init method and additional devices then loaded.
Are there any immediate problems with this kind of approach, or
possibly it's already supported in some way?
Thanks,
Patrick
*The i2c bus numbering can be altered, but typically a BMC's
device-tree uses aliases to ensure consistency of i2c-bus numbering
between configurations.
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