Re: [PATCH v1 0/2] Add support for Xilinx ZynqMP SoC

["Edgar E. Iglesias" <edgar.iglesias@gmail.com>]

On Fri, Mar 06, 2015 at 09:44:16AM +0000, Ian Campbell wrote:
> On Fri, 2015-03-06 at 11:31 +1000, Edgar E. Iglesias wrote:
> > On Thu, Mar 05, 2015 at 04:50:15PM +0000, Ian Campbell wrote:
> > > On Thu, 2015-03-05 at 18:27 +1000, Edgar E. Iglesias wrote:
> > > > From: "Edgar E. Iglesias" <edgar.iglesias@xilinx.com>
> > > > 
> > > > Adds support for the Cadence UART in Xilinx ZynqMP. The
> > > > rest of the ZynqMP platform is discovered via device-tree.
> > > 
> > > Is it fully discovered and working out of the box? That would be ....
> > > awesome!
> > 
> > Yes it would be awesome if we can keep it like that :-)
> 
> I suppose you are seeing the "WARNING: Unrecognized/unsupported device
> tree compatible list" message?

Yes, thats right.

> 
> I wonder if we should either remove or tone down that warning, now that
> we have a platform which genuinely doesn't require any platform specific
> code. I think we probably want to say something so in bug reports we
> know what is happening, maybe just something like "Platform: Generic
> System".


Sounds good to me, I can send a follow up patch for that.

> 
> > It's possible that we will need to add platform code in the future
> > as we test out more features. In particular we'll likely need to do
> > something around power/clock management.
> 
> Yes, this is something of an open problem for us, and one which I'm
> unsure how to solve without some platform specific code in each case.
> 
> Most power/clock management should be deferred to the h/w domain which
> is managing the I/O peripherals (likely dom0) but we need some way to
> filter its activities to keep e.g. the CPU and UART (or in reality any
> h/w block Xen itself is using, which isn't many fortunately) clocks on.
> 
> http://bugs.xenproject.org/xen/bug/45 is a related bug.

Very interesting, thanks.

There is another dimenson to the power/clock problem. The ZynqMP has a
runtime programmable TrustZone system partitioning block in the interconnect.
Something similar to ARMs TZASC. This allows you to program the
Secure/Non-Secure device partitioning for example at boot time.
Depending on the split, it might not be OK to give NS Linux or even
NS XEN direct access to the power/clock configuration registers.
I.e, we don't want NS Linux to power down a device currently in use
by a Trusted OS.

What we are considering is an extension to the PSCI approach, an SMC
interface to expose the low level power/clock operations.

Linux can still have all the smart control logic for Power Management
but an SMC interface would allow the various layers (XEN EL2,
ARM trusted firmware EL3) to filter or emulate the various requests.

Ofcourse, the devil will be in the details...

It would be interesting to hear your and others thought on that kind
of approach.


> 
> > > Do you have any links to any more information about this platform (I'm
> > > just curious).
> > 
> > This one is a good starting point with follow-up links:
> > http://www.xilinx.com/products/technology/ultrascale-mpsoc.html
> > 
> > The short version is that the ZynqMP is a chip including both a hard SoC part
> > (PS, Programmable System) and a "soft" Programmable Logic (PL) FPGA part.
> > In terms of Virtualization, the hard PS part has quad Cortex-A53s with
> > EL2 enabled and an SMMU to allow secure device-passthrough of DMA capable devices.
> 
> That sounds like a pretty sweet platform, thanks!
> 
> > For early access there are two platforms available, an FPGA based
> > emulation platform (EP108) and a modified version of QEMU. XEN can run
> > on both those platforms.
> > 
> > 
> > > Also, if you could find the time to add a wikipage as a child of
> > > http://wiki.xenproject.org/wiki/Xen_ARM_with_Virtualization_Extensions
> > > (like for the other platforms) and add it to the h/w table on the main
> > > page that would be great.
> > > 
> > > The wiki is locked down because of spammers, once you've created an
> > > account either drop me a line or fill in the form
> > > http://xenproject.org/component/content/article/100-misc/145-request-to-be-made-a-wiki-editor.html and someone will enable write access for you.
> > 
> > Yes, I'm happy to update the wiki. I've created a user (edgar_igl) and filled out the form.
> 
> I've just seen the form entry and added the write bit to "edgar_igl".
> Thanks!

Thanks!

Best regards,
Edgar