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authorGregory Fong <gregory.0xf0@gmail.com>2015-02-03 18:49:26 -0800
committerJonathan Corbet <corbet@lwn.net>2015-02-27 14:54:55 -0700
commitdce12391d70d24d428def2f5fc600a3b1f791ca6 (patch)
treeb2bf6217ace4b44017982185d0d294e1b78616d8
parentc517d838eb7d07bbe9507871fab3931deccff539 (diff)
downloadlinux-dce12391d70d24d428def2f5fc600a3b1f791ca6.tar.bz2
Documentation: arm: Update for DT-only platforms
The documentation specified that a machine type is mandatory and made that assumption in a few places. However, for DT-only platforms, the current advice is that no machine type should be registered, so update accordingly. Signed-off-by: Gregory Fong <gregory.0xf0@gmail.com> Signed-off-by: Jonathan Corbet <corbet@lwn.net>
-rw-r--r--Documentation/arm/Booting9
-rw-r--r--Documentation/arm/README15
2 files changed, 18 insertions, 6 deletions
diff --git a/Documentation/arm/Booting b/Documentation/arm/Booting
index 371814a36719..83c1df2fc758 100644
--- a/Documentation/arm/Booting
+++ b/Documentation/arm/Booting
@@ -58,13 +58,18 @@ serial format options as described in
--------------------------
Existing boot loaders: OPTIONAL
-New boot loaders: MANDATORY
+New boot loaders: MANDATORY except for DT-only platforms
The boot loader should detect the machine type its running on by some
method. Whether this is a hard coded value or some algorithm that
looks at the connected hardware is beyond the scope of this document.
The boot loader must ultimately be able to provide a MACH_TYPE_xxx
-value to the kernel. (see linux/arch/arm/tools/mach-types).
+value to the kernel. (see linux/arch/arm/tools/mach-types). This
+should be passed to the kernel in register r1.
+
+For DT-only platforms, the machine type will be determined by device
+tree. set the machine type to all ones (~0). This is not strictly
+necessary, but assures that it will not match any existing types.
4. Setup boot data
------------------
diff --git a/Documentation/arm/README b/Documentation/arm/README
index aea34095cdcf..9d1e5b2c92e6 100644
--- a/Documentation/arm/README
+++ b/Documentation/arm/README
@@ -185,13 +185,20 @@ Kernel entry (head.S)
board devices are used, or the device is setup, and provides that
machine specific "personality."
- This fine-grained machine specific selection is controlled by the machine
- type ID, which acts both as a run-time and a compile-time code selection
- method.
+ For platforms that support device tree (DT), the machine selection is
+ controlled at runtime by passing the device tree blob to the kernel. At
+ compile-time, support for the machine type must be selected. This allows for
+ a single multiplatform kernel build to be used for several machine types.
- You can register a new machine via the web site at:
+ For platforms that do not use device tree, this machine selection is
+ controlled by the machine type ID, which acts both as a run-time and a
+ compile-time code selection method. You can register a new machine via the
+ web site at:
<http://www.arm.linux.org.uk/developer/machines/>
+ Note: Please do not register a machine type for DT-only platforms. If your
+ platform is DT-only, you do not need a registered machine type.
+
---
Russell King (15/03/2004)