doc: qfw man-page

Provide a man-page for the qfw command.

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>

doc/usage/index.rst

@@ -28,5 +28,6 @@ Shell commands
    loady
    mbr
    pstore
+   qfw
    sbi
    true

doc/usage/qfw.rst

@@ -0,0 +1,89 @@
+.. SPDX-License-Identifier: GPL-2.0+
+
+qfw command
+===========
+
+Synopsis
+--------
+
+::
+
+    qfw list
+    qfw cpus
+    qfw load [kernel_addr [initrd_addr]]
+
+Description
+-----------
+
+The *qfw* command is used to retrieve information form the QEMU firmware.
+
+The *qfw list* sub-command displays the QEMU firmware files.
+
+The *qfw cpus* sub-command displays the available CPUs.
+
+The *qfw load* command is used to load a kernel and an initial RAM disk.
+
+kernel_addr
+    address to which the file specified by the -kernel parameter of QEMU shall
+    be loaded. Defaults to environment variable *loadaddr* and further to
+    the value of *CONFIG_LOADADDR*.
+
+initrd_addr
+    address to which the file specified by the -initrd parameter of QEMU shall
+    be loaded. Defaults to environment variable *ramdiskaddr* and further to
+    the value of *CONFIG_RAMDISK_ADDR*.
+
+Examples
+--------
+
+QEMU firmware files are listed via the *qfw list* command:
+
+::
+
+    => qfw list
+    etc/boot-fail-wait
+    etc/smbios/smbios-tables
+    etc/smbios/smbios-anchor
+    etc/e820
+    genroms/kvmvapic.bin
+    genroms/linuxboot.bin
+    etc/system-states
+    etc/acpi/tables
+    etc/table-loader
+    etc/tpm/log
+    etc/acpi/rsdp
+    bootorder
+
+The available CPUs can be shown via the *qfw cpus* command:
+
+::
+
+    => qfw cpu
+    2 cpu(s) online
+
+The *-kernel* and *-initrd* parameters allow to specify a kernel and an
+initial RAM disk for QEMU:
+
+.. code-block:: bash
+
+   $ qemu-system-x86_64 -machine pc-i440fx-2.5 -bios u-boot.rom -m 1G \
+       -nographic -kernel vmlinuz -initrd initrd
+
+Now the kernel and the initial RAM disk can be loaded to the U-Boot memory via
+the *qfw load* command and booted thereafter.
+
+::
+
+    => qfw load ${kernel_addr_r} ${ramdisk_addr_r}
+    loading kernel to address 0000000001000000 size 5048f0 initrd 0000000004000000 size 3c94891
+    => zboot 1000000 5048f0 4000000 3c94891
+    Valid Boot Flag
+    Magic signature found
+    Linux kernel version 4.19.0-14-amd64 (debian-kernel@lists.debian.org) #1 SMP Debian 4.19.171-2 (2021-01-30)
+    Building boot_params at 0x00090000
+    Loading bzImage at address 100000 (5260160 bytes)
+
+Configuration
+-------------
+
+The qfw command is only available if CONFIG_CMD_QFW=y.