Merge branch 'master' of git://git.denx.de/u-boot-spi

[oweals/u-boot.git] / doc / driver-model / README.txt

diff --git a/doc/driver-model/README.txt b/doc/driver-model/README.txt
index d6fa5c4857934264dae874613370c0b3981010bd..07b120d51218dd7d2b494fc7cbdf2c49f7efdcca 100644 (file)
--- a/doc/driver-model/README.txt
+++ b/doc/driver-model/README.txt
@@ -449,6 +449,15 @@ The driver model tree is intended to mirror that of the device tree. The
 root driver is at device tree offset 0 (the root node, '/'), and its
 children are the children of the root node.
 
+In order for a device tree to be valid, the content must be correct with
+respect to either device tree specification
+(https://www.devicetree.org/specifications/) or the device tree bindings that
+are found in the doc/device-tree-bindings directory.  When not U-Boot specific
+the bindings in this directory tend to come from the Linux Kernel.  As such
+certain design decisions may have been made already for us in terms of how
+specific devices are described and bound.  In most circumstances we wish to
+retain compatibility without additional changes being made to the device tree
+source files.
 
 Declaring Uclasses
 ------------------
@@ -821,13 +830,24 @@ Pre-Relocation Support
 ----------------------
 
 For pre-relocation we simply call the driver model init function. Only
-drivers marked with DM_FLAG_PRE_RELOC or the device tree
-'u-boot,dm-pre-reloc' flag are initialised prior to relocation. This helps
-to reduce the driver model overhead.
+drivers marked with DM_FLAG_PRE_RELOC or the device tree 'u-boot,dm-pre-reloc'
+property are initialised prior to relocation. This helps to reduce the driver
+model overhead. This flag applies to SPL and TPL as well, if device tree is
+enabled (CONFIG_OF_CONTROL) there.
+
+Note when device tree is enabled, the device tree 'u-boot,dm-pre-reloc'
+property can provide better control granularity on which device is bound
+before relocation. While with DM_FLAG_PRE_RELOC flag of the driver all
+devices with the same driver are bound, which requires allocation a large
+amount of memory. When device tree is not used, DM_FLAG_PRE_RELOC is the
+only way for statically declared devices via U_BOOT_DEVICE() to be bound
+prior to relocation.
 
 It is possible to limit this to specific relocation steps, by using
 the more specialized 'u-boot,dm-spl' and 'u-boot,dm-tpl' flags
-in the devicetree.
+in the device tree node. For U-Boot proper you can use 'u-boot,dm-pre-proper'
+which means that it will be processed (and a driver bound) in U-Boot proper
+prior to relocation, but will not be available in SPL or TPL.
 
 Then post relocation we throw that away and re-init driver model again.
 For drivers which require some sort of continuity between pre- and