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-rw-r--r--docs/system/riscv/microchip-icicle-kit.rst54
1 files changed, 47 insertions, 7 deletions
diff --git a/docs/system/riscv/microchip-icicle-kit.rst b/docs/system/riscv/microchip-icicle-kit.rst
index 54ced66..817d2aec 100644
--- a/docs/system/riscv/microchip-icicle-kit.rst
+++ b/docs/system/riscv/microchip-icicle-kit.rst
@@ -47,13 +47,13 @@ The user provided DTB should have the following requirements:
QEMU follows below truth table to select which payload to execute:
-===== ========== =======
--bios -kernel payload
-===== ========== =======
- N N HSS
- Y don't care HSS
- N Y kernel
-===== ========== =======
+===== ========== ========== =======
+-bios -kernel -dtb payload
+===== ========== ========== =======
+ N N don't care HSS
+ Y don't care don't care HSS
+ N Y Y kernel
+===== ========== ========== =======
The memory is set to 1537 MiB by default which is the minimum required high
memory size by HSS. A sanity check on ram size is performed in the machine
@@ -106,4 +106,44 @@ HSS output is on the first serial port (stdio) and U-Boot outputs on the
second serial port. U-Boot will automatically load the Linux kernel from
the SD card image.
+Direct Kernel Boot
+------------------
+
+Sometimes we just want to test booting a new kernel, and transforming the
+kernel image to the format required by the HSS bootflow is tedious. We can
+use '-kernel' for direct kernel booting just like other RISC-V machines do.
+
+In this mode, the OpenSBI fw_dynamic BIOS image for 'generic' platform is
+used to boot an S-mode payload like U-Boot or OS kernel directly.
+
+For example, the following commands show building a U-Boot image from U-Boot
+mainline v2021.07 for the Microchip Icicle Kit board:
+
+.. code-block:: bash
+
+ $ export CROSS_COMPILE=riscv64-linux-
+ $ make microchip_mpfs_icicle_defconfig
+
+Then we can boot the machine by:
+
+.. code-block:: bash
+
+ $ qemu-system-riscv64 -M microchip-icicle-kit -smp 5 -m 2G \
+ -sd path/to/sdcard.img \
+ -nic user,model=cadence_gem \
+ -nic tap,ifname=tap,model=cadence_gem,script=no \
+ -display none -serial stdio \
+ -kernel path/to/u-boot/build/dir/u-boot.bin \
+ -dtb path/to/u-boot/build/dir/u-boot.dtb
+
+CAVEATS:
+
+* Check the "stdout-path" property in the /chosen node in the DTB to determine
+ which serial port is used for the serial console, e.g.: if the console is set
+ to the second serial port, change to use "-serial null -serial stdio".
+* The default U-Boot configuration uses CONFIG_OF_SEPARATE hence the ELF image
+ ``u-boot`` cannot be passed to "-kernel" as it does not contain the DTB hence
+ ``u-boot.bin`` has to be used which does contain one. To use the ELF image,
+ we need to change to CONFIG_OF_EMBED or CONFIG_OF_PRIOR_STAGE.
+
.. _HSS: https://github.com/polarfire-soc/hart-software-services