Firmware update for auxiliary components

[Richard Hughes]

On Tue, 11 Jan 2022 at 01:31, Derek Mantey <derekma at microsoft.com> wrote:
> I tried to pull the changes in but ran into some build issues.

Ohh? If you share them I might be able to help. I know fwpud is quite
aggressive with some of it's deps, but they should be all up to date
in oe-meta.

> could you tell me a little more about the interfaces that the fwupd uses?

No problem; but I suspect the answer is "all of them" :)

>  Is it searching the device tree for devices that it can update?  Is it searching the busses directly?  Or is there a way to give hints for devices to update?

It does all of those things. In general, a "plugin" in fwupd just knows how to:

 * enumerate (discover) the device, e.g. looking at the ESRT, looking
at files in /sys, using udev to find a device, or claiming an
interface on a USB device
 * Install a blob of firmware on that device node
 * (optionally) switch the device into, and out-of bootloader mode

There's quite a lot more, but it's all basically optional -- there's a
little tutorial available here:
https://fwupd.github.io/libfwupdplugin/tutorial.html

In reality, the best way to see how it all works is to look at the
code, for instance,
https://github.com/fwupd/fwupd/blob/main/plugins/nvme/fu-nvme-device.c
is <500 lines on how to properly enumerate and update a NVMe drive.

> For example, we have a CPLD on our board (see the Open Compute DC-SCM spec).  We don't currently have that listed in our device tree as it is just sitting on a generic SPI bus.

The best way is to make it discoverable, as you don't need to add a
quirk file for each of the system boards that you want to support,
e.g. put it in an ACPI table or DT somewhere. If that's not possible,
you can add a "quirk" to fwupd to say "for this hardware do this",
e.g. https://github.com/fwupd/fwupd/blob/main/plugins/superio/superio.quirk#L55
although this isn't awesome as you have to update fwupd every time you
have a new board to support. Ideally you could ask an embedded
controller somewhere "what CPLDs are connected" and get back all the
data you need.

Richard