docs/LoongArch: Add booting description

1, Describe the information passed from BootLoader to kernel.
2, Describe the meaning and values of the kernel image header field.

Suggested-by: Xiaotian Wu <wuxiaotian@loongson.cn>
Signed-off-by: Yanteng Si <siyanteng@loongson.cn>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>

diff --git a/Documentation/loongarch/booting.rst b/Documentation/loongarch/booting.rst
new file mode 100644 (file)
index 0000000..91eccd4
--- /dev/null
+++ b/Documentation/loongarch/booting.rst
@@ -0,0 +1,42 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+=======================
+Booting Linux/LoongArch
+=======================
+
+:Author: Yanteng Si <siyanteng@loongson.cn>
+:Date:   18 Nov 2022
+
+Information passed from BootLoader to kernel
+============================================
+
+LoongArch supports ACPI and FDT. The information that needs to be passed
+to the kernel includes the memmap, the initrd, the command line, optionally
+the ACPI/FDT tables, and so on.
+
+The kernel is passed the following arguments on `kernel_entry` :
+
+      - a0 = efi_boot: `efi_boot` is a flag indicating whether
+        this boot environment is fully UEFI-compliant.
+
+      - a1 = cmdline: `cmdline` is a pointer to the kernel command line.
+
+      - a2 = systemtable: `systemtable` points to the EFI system table.
+        All pointers involved at this stage are in physical addresses.
+
+Header of Linux/LoongArch kernel images
+=======================================
+
+Linux/LoongArch kernel images are EFI images. Being PE files, they have
+a 64-byte header structured like::
+
+       u32     MZ_MAGIC                /* "MZ", MS-DOS header */
+       u32     res0 = 0                /* Reserved */
+       u64     kernel_entry            /* Kernel entry point */
+       u64     _end - _text            /* Kernel image effective size */
+       u64     load_offset             /* Kernel image load offset from start of RAM */
+       u64     res1 = 0                /* Reserved */
+       u64     res2 = 0                /* Reserved */
+       u64     res3 = 0                /* Reserved */
+       u32     LINUX_PE_MAGIC          /* Magic number */
+       u32     pe_header - _head       /* Offset to the PE header */

diff --git a/Documentation/loongarch/index.rst b/Documentation/loongarch/index.rst
index aaba648..c779bfa 100644 (file)
--- a/Documentation/loongarch/index.rst
+++ b/Documentation/loongarch/index.rst
@@ -9,6 +9,7 @@ LoongArch Architecture
    :numbered:
 
    introduction
+   booting
    irq-chip-model
 
    features