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

Simon Glass
2022-08-02T03:08:19Z

Hi Sudeep,

On Mon, 1 Aug 2022 at 13:28, Sudeep Holla <sudeep.holla@arm.com> wrote:
>
> 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.

Oh well my understanding of Open Firmware was that the firmware did
the probing and passed the info to the OS.

>
> > 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

Yes it is something I am becoming more and more concerned about.

> 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.

I'm not sure either. In particular I'm not sure why it would be easier
to update whatever the FF-A software is than to update the DT, since
presumably they are both in the firmware.

I am talking about an issue in general and the same issue in
particular with this series.

Can I suggest resending this series with a change log for each patch.
Also please try to avoid #ifdefs and make sure to include
documentation in doc/ including how this relates to the UEFI
firmware-update effort that ARM/Linaro is undertaking. Also, what
happened to the tests / sandbox driver?

Regards,
Simon