[U-Boot,v2,05/10] doc: Document how to apply fdt overlays

Submitted by Pantelis Antoniou on Aug. 11, 2017, 8:52 a.m.


Message ID 1502441568-22896-6-git-send-email-pantelis.antoniou@konsulko.com
State New
Delegated to: Simon Glass
Headers show

Commit Message

Pantelis Antoniou Aug. 11, 2017, 8:52 a.m.
We have the capability to apply overlays on the command line but
we didn't have a document explaining how.

Signed-off-by: Pantelis Antoniou <pantelis.antoniou@konsulko.com>
 doc/README.fdt-overlays | 37 +++++++++++++++++++++++++++++++++++++
 1 file changed, 37 insertions(+)
 create mode 100644 doc/README.fdt-overlays

Patch hide | download patch | download mbox

diff --git a/doc/README.fdt-overlays b/doc/README.fdt-overlays
new file mode 100644
index 0000000..ee868ec
--- /dev/null
+++ b/doc/README.fdt-overlays
@@ -0,0 +1,37 @@ 
+U-Boot FDT Overlay usage (without FIT images)
+FDT overlays are now available for use even without FIT images.
+It is not as automagic as with FIT images though and require a few
+manual steps.
+1. Figure out where to place both the base device tree blob and the
+overlay. Make sure you have enough space to grow the base tree without
+overlapping anything.
+=> setenv fdtaddr 0x87f00000
+=> setenv fdtovaddr 0x87fc0000
+2. Load the base blob and overlay blobs
+=> load ${devtype} ${bootpart} ${fdtaddr} ${bootdir}/base.dtb
+=> load ${devtype} ${bootpart} ${fdtovaddr} ${bootdir}/overlay.dtb
+3. Set it as the working fdt tree.
+=> fdtaddr $fdtaddr
+4. Grow it enough so it can 'fit' all the applied overlays
+=> fdt resize 8192
+5. You are now ready to apply the overlay.
+=> fdt apply $fdtovaddr
+Please note that in case of an error, both the base and overlays are going
+to be invalidated, so keep copies to avoid reloading.
+Pantelis Antoniou