Re: [PATCH 1/1] added support for zynq7000-fpga-manager

[Michael Tretter <m.tretter@pengutronix.de>]

Hi Michael,

On Tue, 30 Mar 2021 12:05:31 +0000, Michael Graichen wrote:
> > I think, it would be fine to use only "zynq" instead of zynqmp for the
> > firmware loader/fpga manager. (I didn't compare the Zynq7000 and ZynqMP low
> > level interfaces for programming the FPGA, yet, but I guess that programming
> > the FPGA on the ZynqMP in EL3 instead of EL2/EL1 is actually the same as on
> > Zynq7000.) I am also ok with treating ZynqMP as a second class citizen in the
> > driver. 
> 
> As I compared
> https://www.xilinx.com/support/documentation/user_guides/ug585-Zynq-7000-TRM.pdf
> page 211ff and
> https://www.xilinx.com/support/documentation/user_guides/ug1085-zynq-ultrascale-trm.pdf
> page 261ff the programming of the PCAP seem to be similar, but PCAP is
> embedded in CSU/PMU on ZynqMP, which looks much more complex then DEVC on
> Zynq7000. But I don't know how much of CSUs functionality is acctually
> needed to programm the FPGA.

The PCAP behave similar and have similar registers and bits, but the register
layouts are completely different. It seems that for programming the FPGA on
the ZynqMP, one would at least have to configure the internal stream switch
and use CSU DMA engine for the image transfer. For encrypted bitstreams, the
AES engine in the CSU has to be used as well.

> 
> Is the CSU within ZynqMP used for something other than programming the
> firmware in barebox?

At the moment, Barebox doesn't directly use the CSU. Barebox is not even
allowed to access the CSU register. It uses SMCs via TF-A to instruct the
PMU-FW to program the FPGA. The PMU-FW then talks to the CSU for actually
programming the FPGA.

If Barebox would run as first stage bootloader, it might use the CSU to read
the PS version or might use some of the authentication/encryption features of
the CSU, but this is currently not the case.

Watch out for the overloaded term "firmware". The firmware manager in the
zynqmp-fpga driver in Barebox is able to _load_ a "firmware", in this case the
FPGA bitstream. The firmware-zynqmp driver is a driver to _talk to_ the PMU
firmware, which is a firmware that is already running on the system.

Michael

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