Linux kernel uses M-mode trap for handling Inter-Hart Communication (IHC).
This patch provides all the required functionalities for this purpose.
Previously, HSS bootloader was required. Now, NuttX is run as the
bootloader providing OpenSBI vendor extensions instead. This setup has
been tested on the following configuration:
- Hart 0 has NuttX in bootloader mode with OpenSBI
- Hart 1 unused
- Hart 2 has NuttX configured at 0xa2000000
- Hart 3 has U-boot / Linux kernel (at 0x80200000)
- Hart 4 has U-boot / Linux kernel (at 0x80200000)
Upon startup, NuttX on hart 0 will initialize SD-card driver, loads
the hart 2 NuttX from the SD-card and loads the U-boot to 0x80200000.
Also the nuttx.sbi -binary is loaded from SD-card into address 0x80000000,
which is also marked as reserved area in the Linux kernel device tree (for
the chuck 0x80000000 - 0x80200000).
Hart 2 NuttX waits until Linux kernel (IHC master) is started. After the
initial handshake, RPMsg / virtIO bus along with the IHC may be used for
proper AMP mode.
Signed-off-by: Eero Nurkkala <eero.nurkkala@offcode.fi>
This provides an example of Asymmetric Multiprocessing (AMP). The
master from Linux sends pings that this NuttX echoes back. The system
uses RPMsg from OpenAMP.
The Inter-Hart Communication module is present in the vendor's software
stack with the tag "2021.11". The software is present on github at the
polarfire-soc project. The following conditions must be met:
1. FPGA programmed with 2021.11 software
2. HSS (Vendor bootloader) with 2021.11 software
3. U-boot and Linux kernel from 2011.11 software
Currently the IHC works as a slave only on the hart number 4.
On the NuttX side, this patch uses rptun that incorporates rpmsg and
virtio. If it used only rpmsg and virtio, the future maintenance would
likely be much heavier. Using rptun also simplifies many things.
Upon success, the master side from Linux may issue an example test:
root@icicle-kit-es-amp:/opt/microchip/amp/rpmsg-pingpong# ./rpmsg-pingpong
However, the rpmsg-pingpong.c (compiled on target with gcc), may need to
be modified as seen below to match the device id:
- char *rpmsg_dev="virtio0.rpmsg-amp-demo-channel.-1.0";
+ char *rpmsg_dev="virtio0.rpmsg-amp-demo-channel.-1.1024";
This work uses a separate linker script. Due to a bug yet unknown to date,
a small NuttX, when loaded by the vendor HSS bootloader, will cause the
Linux kernel to hang at boot. Thus, the binary size is increased with
a section 'filler_area' whose only purpose is to increase the image size
so that the Linux kernel will boot up.
Signed-off-by: Eero Nurkkala <eero.nurkkala@offcode.fi>
