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-rw-r--r--Documentation/arm/Booting42
1 files changed, 32 insertions, 10 deletions
diff --git a/Documentation/arm/Booting b/Documentation/arm/Booting
index 0c1f475fdf36..371814a36719 100644
--- a/Documentation/arm/Booting
+++ b/Documentation/arm/Booting
@@ -18,7 +18,8 @@ following:
2. Initialise one serial port.
3. Detect the machine type.
4. Setup the kernel tagged list.
-5. Call the kernel image.
+5. Load initramfs.
+6. Call the kernel image.
1. Setup and initialise RAM
@@ -120,12 +121,27 @@ tagged list.
The boot loader must pass at a minimum the size and location of the
system memory, and the root filesystem location. The dtb must be
placed in a region of memory where the kernel decompressor will not
-overwrite it. The recommended placement is in the first 16KiB of RAM
-with the caveat that it may not be located at physical address 0 since
-the kernel interprets a value of 0 in r2 to mean neither a tagged list
-nor a dtb were passed.
+overwrite it, whilst remaining within the region which will be covered
+by the kernel's low-memory mapping.
-5. Calling the kernel image
+A safe location is just above the 128MiB boundary from start of RAM.
+
+5. Load initramfs.
+------------------
+
+Existing boot loaders: OPTIONAL
+New boot loaders: OPTIONAL
+
+If an initramfs is in use then, as with the dtb, it must be placed in
+a region of memory where the kernel decompressor will not overwrite it
+while also with the region which will be covered by the kernel's
+low-memory mapping.
+
+A safe location is just above the device tree blob which itself will
+be loaded just above the 128MiB boundary from the start of RAM as
+recommended above.
+
+6. Calling the kernel image
---------------------------
Existing boot loaders: MANDATORY
@@ -136,11 +152,17 @@ is stored in flash, and is linked correctly to be run from flash,
then it is legal for the boot loader to call the zImage in flash
directly.
-The zImage may also be placed in system RAM (at any location) and
-called there. Note that the kernel uses 16K of RAM below the image
-to store page tables. The recommended placement is 32KiB into RAM.
+The zImage may also be placed in system RAM and called there. The
+kernel should be placed in the first 128MiB of RAM. It is recommended
+that it is loaded above 32MiB in order to avoid the need to relocate
+prior to decompression, which will make the boot process slightly
+faster.
+
+When booting a raw (non-zImage) kernel the constraints are tighter.
+In this case the kernel must be loaded at an offset into system equal
+to TEXT_OFFSET - PAGE_OFFSET.
-In either case, the following conditions must be met:
+In any case, the following conditions must be met:
- Quiesce all DMA capable devices so that memory does not get
corrupted by bogus network packets or disk data. This will save