rpi: move plat_helpers.S to common ...

The plat_helpers.S file was almost identical between its RPi3 and RPi4
versions. Unify the two files, moving it into the common/ directory.

This adds a plat_rpi_get_model() function, which can be used to trigger
RPi4 specific action, detected at runtime. We use that to do the RPi4
specific L2 cache initialisation.

Change-Id: I2295704fd6dde7c76fe83b6d98c7bf998d4bf074
Signed-off-by: Andre Przywara <andre.przywara@arm.com>

rpi: console: Autodetect Mini-UART vs. PL011 configuration ...

The Raspberry Pi has two different UART devices pin-muxed to GPIO 14&15:
One ARM PL011 one and the 8250 compatible "Mini-UART".
A dtoverlay parameter in config.txt will tell the firmware to switch
between the two: it will setup the right clocks and will configure the
pinmuxes accordingly.

To autodetect the user's choice, we read the pinmux register and check
its setting: ALT5 (0x2) means the Mini-UART is used, ALT0 (0x4) points
to the PL011.
Based on that we select the UART driver to initialise.

This will allow console output in any case.

Change-Id: I620d3ce68de6c6576599f2a405636020e1fd1376
Signed-off-by: Andre Przywara <andre.przywara@arm.com>

rpi: Allow using PL011 UART for RPi3/RPi4 ...

The Broadcom 283x SoCs feature multiple UARTs: the mostly used
"Mini-UART", which is an 8250 compatible IP, and at least one PL011.
While the 8250 is usually used for serial console purposes, it suffers
from a design flaw, where its clock depends on the VPU clock, which can
change at runtime. This will reliably mess up the baud rate.
To avoid this problem, people might choose to use the PL011 UART for
the serial console, which is pin-mux'ed to the very same GPIO pins.
This can be done by adding "miniuart-bt" to the "dtoverlay=" line in
config.txt.

To prepare for this situation, use the newly gained freedom of sharing
one console_t pointer across different UART drivers, to introduce the
option of choosing the PL011 for the console.

This is for now hard-coded to choose the Mini-UART by default.
A follow-up patch will introduce automatic detection.

Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Change-Id: I8cf2522151e09ff4ff94a6d396aec6fc4b091a05

rpi4: Amend DTB to advertise PSCI ...

The device tree provided by the official Raspberry Pi firmware uses
spin tables for SMP bringup.

One of the benefit of having TF-A is that it provides PSCI services, so
let's rewrite the DTB to advertise PSCI instead of spin tables.
This uses the (newly exported) routine from the QEMU platform port.

Change-Id: Ifddcb14041ca253a333f8c2d5e97a42db152470c
Signed-off-by: Andre Przywara <andre.przywara@arm.com>

rpi4: Determine BL33 entry point at runtime ...

Now that we have the armstub magic value in place, the GPU firmware will
write the kernel load address (and DTB address) into our special page,
so we can always easily access the actual location without hardcoding
any addresses into the BL31 image.

Make the compile-time defined PRELOADED_BL33_BASE macro optional, and
read the BL33 entry point from the magic location, if the macro was not
defined. We do the same for the DTB address.

This also splits the currently "common" definition of
plat_get_ns_image_entrypoint() to be separate between RPi3 and RPi4.

Change-Id: I6f26c0adc6fce2df47786b271c490928b4529abb
Signed-off-by: Andre Przywara <andre.przywara@arm.com>

rpi4: Accommodate "armstub8.bin" header at the beginning of BL31 image ...

The Raspberry Pi GPU firmware checks for a magic value at offset 240
(0xf0) of the armstub8.bin image it loads. If that value matches,
it writes the kernel load address and the DTB address into subsequent
memory locations.
We can use these addresses to avoid hardcoding these values into the BL31
image, to make it more flexible and a drop-in replacement for the
official armstub8.bin.

Reserving just 16 bytes at offset 240 of the final image file is not easily
possible, though, as this location is in the middle of the generic BL31
entry point code.
However we can prepend an extra section before the actual BL31 image, to
contain the magic and addresses. This needs to be 4KB, because the
actual BL31 entry point needs to be page aligned.

Use the platform linker script hook that the generic code provides, to
add an almost empty 4KB code block before the entry point code. The very
first word contains a branch instruction to jump over this page, into
the actual entry code.
This also gives us plenty of room for the SMP pens later.

Change-Id: I38caa5e7195fa39cbef8600933a03d86f09263d6
Signed-off-by: Andre Przywara <andre.przywara@arm.com>

Add basic support for Raspberry Pi 4 ...

The Raspberry Pi 4 is a single board computer with four Cortex-A72
cores. From a TF-A perspective it is quite similar to the Raspberry Pi
3, although it comes with more memory (up to 4GB) and has a GIC.

This initial port though differs quite a lot from the existing rpi3
platform port, mainly due to taking a much simpler and more robust
approach to loading the non-secure payload:
The GPU firmware of the SoC, which is responsible for initial platform
setup (including DRAM initialisation), already loads the kernel, device
tree and the "armstub" into DRAM. We take advantage of this, by placing
just a BL31 component into the armstub8.bin component, which will be
executed first, in AArch64 EL3.
The non-secure payload can be a kernel or a boot loader (U-Boot or
EDK-2), disguised as the "kernel" image and loaded by the GPU firmware.

So this is just a BL31-only port, which directly drops into EL2
and executes whatever has been loaded as the "kernel" image, handing
over the DTB address in x0.

Change-Id: I636f4d1f661821566ad9e341d69ba36f6bbfb546
Signed-off-by: Andre Przywara <andre.przywara@arm.com>