Re: [PATCH 0/6] introduce Arm FF-A support

Sudeep Holla
2022-08-01T19:28:21Z

On Mon, Aug 01, 2022 at 01:13:23PM -0600, Simon Glass wrote:
> On Wed, 13 Apr 2022 at 10:46, Tom Rini <trini@konsulko.com> wrote:
> >
> > How is it both discoverable and doesn't have a device tree node, in the
> > kernel?
>
> Also, if it is discoverable, we can still use U-Boot to discover it
> and then pass the info to Linux in the DT.
>

Why ? Linux can discover the presence of the feature with a simple SMCCC
based query. We don't need any DT bindings for this particular feature.
Not sure if you are talking in general or in the context of $subject
feature in the kernel.

> I am seeing several series which don't have 'proper' DT bindings in
> Linux. First I heard it was for legacy reasons, but now I am hearing
> something different. For U-Boot, we really do need to have DT bindings
> for devices. All this ad-hoc creation of stuff makes things hard to
> discover, adds to code size and makes things like of-platdata
> impossible.
>

I may not have the complete picture here. If you are saying that every
feature in the u-boot needs DT for some reason, then that's U-boot's
limitation or restriction. But just the presence of node means nothing
until the corresponding feature is queried and confirmed to be present
in the firmware. That is very important as we can't skip the query stage
just because of presence of some DT node for this.

> Furthermore, if the bindings affect U-Boot, then the U-Boot project
> should have a say in what is being done there, not just be downstream
> of all such changes.
>

I still think you talking about some issue in general and it doesn't
apply in this case. The new firmware interfaces are designed to be
discoverable which is the main advantage over any non discoverable
hardware and/or firmware interface. One main advantage I see is that we
don't need any DT bindings which makes the firmware upgrades must simpler
as the users can query the interface and know exactly what they need
instead of relying on DT node which may get stale if not updated with the
firmware update. I am not sure if whatever I am writing here is relevant
to what your concerns are as I think I haven't understood them fully.

--
Regards,
Sudeep