Re: [PATCH v8 03/10] arm_ffa: introduce Arm FF-A low-level driver

Tom Rini
2023-01-19T17:21:58Z

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On Thu, Jan 19, 2023 at 05:09:45PM +0000, Sudeep Holla wrote:
> On Thu, Jan 19, 2023 at 11:57:44AM -0500, Tom Rini wrote:
> >
> > But it's also true that at run-time, within U-Boot, we can modify the
> > device tree we have, with live tree yes? So, the whole series in
> > question here can be done without modifying the base DT and getting in
> > to the further discussions that doing so entails. The assertion is that
> > the software discoverable bus here is sufficient to not need DT, so, OK,
> > lets go.
>
> OK, may be I am not up-to-date on the U-Boot. IIUC, the modifications
> done in the DT by U-Boot is mostly for consumption by the next stage
> loader/OS and not for self-consumption. But if it is for self consumption,
> then good. It helps especially for the subnodes(as Simon referred) or the
> partitions that can be discovered at run-time using FF-A interface.
>
> As mentioned I am not again DT, it is just not needed and especially
> for subnodes it could result in inconsistency b/w what is in DT and
> what the firmware provides. As mentioned in previous response, having a
> simple node that Simon provided as example earlier is fine by me if that
> is the only option to make progress as I just feel it is redundant and
> one can say not scalable(but that is debatable again 😄).
>
> In short, I am not concerned about having simple node, just don't like
> to see entire FF-A bus enumerated in DT as subnodes for reasons mentioned
> already.

So there's two parts to this discussion. The first of which has been, do
Simon and I agree with the direction of defining a software discoverable
bus rather than using device tree to describe it. To which the answer is
no, and also neither camp seems likely to convince the other. The second
part of the discussion is what can we practically do about it. To which
the answer is that I believe the live tree support (see
https://u-boot.readthedocs.io/en/latest/develop/driver-model/livetree.html)
should allow for the FF-A bus support to be integrated with U-Boot,
without having to add something to the base device tree. And we can
evaluate down the line if our fears (or at least mine) were unfounded or
not.

--
Tom

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