[NOT-FOR-UPSTREAM] Add build instructions

For convenience this also adds a small visionfive_defconfig and the
firmware needed for the brcmfmac driver along with the signed regulatory
database.

The firmware is from the linux-firmware repo and the regulatory database
from the wireless-regdb Fedora package.

Signed-off-by: Geert Uytterhoeven <[email protected]>
Signed-off-by: Drew Fustini <[email protected]>
Signed-off-by: Emil Renner Berthing <[email protected]>

README.md

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+# Linux kernel for StarFive's JH7100 RISC-V SoC
+
+## What is this?
+
+The [JH7100][soc] is a Linux-capable dual-core 64bit RISC-V SoC and this tree
+is meant to collect all the in-development patches for running Linux on boards
+using this. So far there are two such boards and both are supported by this tree:
+
+1) [StarFive VisionFive][visionfive]
+2) [BeagleV Starlight Beta][starlight]
+
+The VisionFive boards aren't quite shipping yet, but you can already
+[register interest][interest] and ask questions on the [forum][].
+
+About 300 BeagleV Starlight Beta boards were sent out to developers in
+April 2021 in preparation for an eventual BeagleV branded board using the
+updated JH7110 chip. The BeagleBoard organization has since [cancelled that
+project][beaglev] though.
+
+
+[visionfive]: https://github.com/starfive-tech/VisionFive
+[interest]: http://starfive.mikecrm.com/doQXj99
+[forum]: https://forum.rvspace.org/c/visionfive/6
+[starlight]: https://github.com/beagleboard/beaglev-starlight
+[soc]: https://github.com/starfive-tech/JH7100_Docs
+[beaglev]: https://beaglev.org/blog/2021-07-30-the-future-of-beaglev-community
+
+## Cross-compiling
+
+Cross-compiling the Linux kernel is surprisingly easy since it doesn't depend
+on any (target) libraries and most distributions already have packages with a
+working cross-compiler. We'll also need a few other tools to build everything:
+```shell
+# Debian/Ubuntu
+sudo apt-get install libncurses-dev libssl-dev bc flex bison make gcc gcc-riscv64-linux-gnu
+# Fedora
+sudo dnf install ncurses-devel openssl openssl-devel bc flex bison make gcc gcc-riscv64-linux-gnu
+# Archlinux
+sudo pacman -S --needed ncurses openssl bc flex bison make gcc riscv64-linux-gnu-gcc
+```
+
+The build system needs to know that we want to cross-compile a kernel for
+RISC-V by setting `ARCH=riscv`. It also needs to know the prefix of our
+cross-compiler using `CROSS_COMPILE=riscv64-linux-gnu-`. Also let's assume
+we're building on an 8-core machine so compilation can be greatly sped up by
+telling make to use all 8 cores with `-j8`.
+
+First we need to configure the kernel though. Linux has a *very* extensive
+configuration system, but you can get a good baseline configuration for the
+boards using:
+```shell
+make -j8 ARCH=riscv CROSS_COMPILE=riscv64-linux-gnu- visionfive_defconfig
+```
+
+There is nothing magic about this configuration other than it has all the
+drivers enabled that are working for the hardware on the boards. In fact it has
+very little extra features enabled which is great for compile times, but you
+are very much encouraged to add additional drivers and configure your kernel
+further using
+```shell
+make -j8 ARCH=riscv CROSS_COMPILE=riscv64-linux-gnu- nconfig
+```
+
+Now compile the whole thing with
+```
+make -j8 ARCH=riscv CROSS_COMPILE=riscv64-linux-gnu-
+```
+
+
+## Installing
+
+Once the build has finished the resulting kernel can be found at
+```shell
+arch/riscv/boot/Image
+```
+You'll also need the matching device tree at
+```shell
+arch/riscv/boot/dts/starfive/jh7100-starfive-visionfive-v1.dtb
+```
+(If you have a Starlight board you should instead be using `jh7100-beaglev-starlight.dtb`.)
+
+These two files should be copied to the boot partition on the SD card. In the
+default [Fedora image][fedora] this is `/dev/mmcblk0p3` and is mounted at `/boot`.
+
+Now add the following entry to the `grub.cfg` file:
+```
+menuentry 'My New Kernel' {
+    linux /Image earlycon console=ttyS0,115200n8 root=/dev/mmcblk0p4 rootwait
+    devicetree /jh7100-starfive-visionfive-v1.dtb
+}
+```
+
+This assumes your root file system is at `/dev/mmcblk0p4` which it is in the
+default [Fedora image][fedora].
+
+The `visionfive_defconfig` doesn't enable modules, but if you enabled them in
+your build you'll also need to install them in `/lib/modules/` on the root file
+system. How to do that best is out of scope for this README though.
+
+[fedora]: https://github.com/starfive-tech/Fedora_on_StarFive/
+
+## Status
+
+#### SoC
+
+- [x] Clock tree
+- [x] Resets
+- [x] Pinctrl/Pinmux
+- [x] GPIO
+- [x] Serial port
+- [x] I2C
+- [x] SPI
+- [x] MMC / SDIO / SD card
+- [x] Random number generator
+- [x] Temperature sensor
+- [x] Ethernet
+- [x] USB
+- [x] DRM driver
+- [x] NVDLA
+- [x] Watchdog
+- [x] PWM DAC for sound through the minijack, only 16kHz samplerate for now
+- [ ] I2S [WIP]
+- [ ] TDM [WIP]
+- [ ] MIPI-DSI [WIP]
+- [ ] MIPI-CSI [WIP]
+- [ ] ISP [WIP]
+- [ ] Video Decode [WIP]
+- [ ] Video Encode [WIP]
+- [ ] QSPI
+- [ ] Security Engine
+- [ ] NNE50
+- [ ] Vision DSP
+
+#### Board
+
+- [x] LED
+- [x] PMIC / Reboot
+- [x] Ethernet PHY
+- [x] HDMI
+- [x] AP6236 Wifi
+- [x] AP6236 Bluetooth, with a [userspace tool][patchram]
+- [x] I2C EEPROM (VisionFive only)
+- [ ] GD25LQ128DWIG (VisionFive) / GD25LQ256D (Starlight) flash
+
+[patchram]: https://github.com/AsteroidOS/brcm-patchram-plus
+
+## Contributing
+
+If you're working on cleaning up or upstreaming some of this or adding support
+for more of the SoC I'd very much like to incorporate it into this tree. Either
+send a pull request, mail or contact Esmil on IRC/Slack.
+
+Also think of this tree mostly as a collection of patches that will hopefully
+mature enough to be submitted upstream eventually. So expect regular rebases.