docs: move generic-loader documentation into the main manual

We might as well surface this useful information in the manual so
users can find it easily. It is a fairly simple conversion to rst with
the only textual fixes being QemuOps to QemuOpts.

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Message-Id: <20210303173642.3805-6-alex.bennee@linaro.org>

MAINTAINERS

@@ -2020,7 +2020,7 @@ M: Alistair Francis <alistair@alistair23.me>
 S: Maintained
 F: hw/core/generic-loader.c
 F: include/hw/core/generic-loader.h
-F: docs/generic-loader.txt
+F: docs/system/generic-loader.rst
 
 Guest Loader
 M: Alex Bennée <alex.bennee@linaro.org>

docs/system/generic-loader.rst

@@ -0,0 +1,117 @@
+..
+   Copyright (c) 2016, Xilinx Inc.
+
+This work is licensed under the terms of the GNU GPL, version 2 or later.  See
+the COPYING file in the top-level directory.
+
+Generic Loader
+--------------
+
+The 'loader' device allows the user to load multiple images or values into
+QEMU at startup.
+
+Loading Data into Memory Values
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+The loader device allows memory values to be set from the command line. This
+can be done by following the syntax below::
+
+   -device loader,addr=<addr>,data=<data>,data-len=<data-len> \
+                   [,data-be=<data-be>][,cpu-num=<cpu-num>]
+
+``<addr>``
+  The address to store the data in.
+
+``<data>``
+  The value to be written to the address. The maximum size of the data
+  is 8 bytes.
+
+``<data-len>``
+  The length of the data in bytes. This argument must be included if
+  the data argument is.
+
+``<data-be>``
+  Set to true if the data to be stored on the guest should be written
+  as big endian data. The default is to write little endian data.
+
+``<cpu-num>``
+  The number of the CPU's address space where the data should be
+  loaded. If not specified the address space of the first CPU is used.
+
+All values are parsed using the standard QemuOps parsing. This allows the user
+to specify any values in any format supported. By default the values
+will be parsed as decimal. To use hex values the user should prefix the number
+with a '0x'.
+
+An example of loading value 0x8000000e to address 0xfd1a0104 is::
+
+    -device loader,addr=0xfd1a0104,data=0x8000000e,data-len=4
+
+Setting a CPU's Program Counter
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+The loader device allows the CPU's PC to be set from the command line. This
+can be done by following the syntax below::
+
+     -device loader,addr=<addr>,cpu-num=<cpu-num>
+
+``<addr>``
+  The value to use as the CPU's PC.
+
+``<cpu-num>``
+  The number of the CPU whose PC should be set to the specified value.
+
+All values are parsed using the standard QemuOpts parsing. This allows the user
+to specify any values in any format supported. By default the values
+will be parsed as decimal. To use hex values the user should prefix the number
+with a '0x'.
+
+An example of setting CPU 0's PC to 0x8000 is::
+
+    -device loader,addr=0x8000,cpu-num=0
+
+Loading Files
+^^^^^^^^^^^^^
+
+The loader device also allows files to be loaded into memory. It can load ELF,
+U-Boot, and Intel HEX executable formats as well as raw images.  The syntax is
+shown below:
+
+    -device loader,file=<file>[,addr=<addr>][,cpu-num=<cpu-num>][,force-raw=<raw>]
+
+``<file>``
+  A file to be loaded into memory
+
+``<addr>``
+  The memory address where the file should be loaded. This is required
+  for raw images and ignored for non-raw files.
+
+``<cpu-num>``
+  This specifies the CPU that should be used. This is an
+  optional argument and will cause the CPU's PC to be set to the
+  memory address where the raw file is loaded or the entry point
+  specified in the executable format header. This option should only
+  be used for the boot image. This will also cause the image to be
+  written to the specified CPU's address space. If not specified, the
+  default is CPU 0. <force-raw> - Setting force-raw=on forces the file
+  to be treated as a raw image. This can be used to load supported
+  executable formats as if they were raw.
+
+All values are parsed using the standard QemuOpts parsing. This allows the user
+to specify any values in any format supported. By default the values
+will be parsed as decimal. To use hex values the user should prefix the number
+with a '0x'.
+
+An example of loading an ELF file which CPU0 will boot is shown below::
+
+    -device loader,file=./images/boot.elf,cpu-num=0
+
+Restrictions and ToDos
+^^^^^^^^^^^^^^^^^^^^^^
+
+At the moment it is just assumed that if you specify a cpu-num then
+you want to set the PC as well. This might not always be the case. In
+future the internal state 'set_pc' (which exists in the generic loader
+now) should be exposed to the user so that they can choose if the PC
+is set or not.
+
+

docs/system/index.rst

@@ -25,6 +25,7 @@ Contents:
    usb
    ivshmem
    linuxboot
+   generic-loader
    vnc-security
    tls
    gdb