Changes between Version 13 and Version 14 of linux/devicetree

Timestamp:

05/11/2022 06:15:31 PM (2 years ago)

Author:

Tim Harvey

Comment:

enhanced fixfdt section

linux/devicetree

@@ -40 +40 @@
 The U-Boot bootloader is responsible for Loading a device-tree, making any adjustments necessary, and passing it to the kernel.
 
-If desired you can use the {{{ftd}}} U-boot command to access/modify the devicetree before the kernel is booted.
+If desired during this process you can use the {{{ftd}}} U-boot command to access/modify the devicetree before the kernel is booted. How and where to do this would depend greatly on the U-Boot bootscript used to boot your OS.
 
 Examples:
+ * Venice: disable PCI:
+{{{
+setenv fsload 'load mmc 2:1'
+run loadfdt && fdt addr $fdt_addr_r
+fdt resize
+fdt set /soc@0/pcie@33800000 status disabled
+}}}
  * Ventana: display the fdt on a NAND flash board:
 {{{#!bash
@@ -50 +57 @@
 fdt print
 }}}
- * Ventana: disable PCI via {{{fixfdt}}} script:
+ * Ventana: disable PCI:
 {{{#!bash
 setenv fsload 'ubifsload'
@@ -59 +66 @@
 }}}
 
-Note some bootloader environments such as Ventana and Venice call a {{{fixfdt}}} script that can make integrating fixups like this into the boot process easy. See [http://trac.gateworks.com/wiki/ventana/bootloader#Specifyinganalternatedevice-treeblobDTB here] for details.
-
+Important notes regarding the 'fdt set' command 'value' parameter:
+ * numbers can be represented as decimal or as hex with a '0x' prefix
+ * an array of cells is specified as a list of numbers enclosed in < and >, ie <0x00112233 4 05>
+ * a byte stream can be represented as a list of numbers enclosed in [ and ], ie [00 11 22 .. nn]
+ * a 32bit integer is a 4-byte MSB stream so a hex value of 0x1 would be represented as [00 00 00 01]
+ * if the value does not start with a < or a [ it is treated as a string (quotes are stripped if present)
+
+
+[=#fixfdt]
+=== fixfdt script
+If using the Gateworks BSP's the {{{fixfdt}}} env variable if set will be run as a script during the process as a feature of the Gateworks boot scripts.
+
+Examples:
+ * Venice: The {{{loadfdt}}} script will load the dt to the address specified in the {{{fdt_addr_r}}} env var
+  - disable PCI via {{{fixfdt}}} script:
+{{{
+setenv fixfdt 'fdt addr $fdt_addr_r; fdt resize; fdt set /soc@0/pcie@33800000 status disabled'
+saveenv
+}}}
+  - limit PCI link to Gen 1 (default is Gen2 for Venice)
+{{{
+setenv fixfdt 'fdt addr $fdt_addr_r; fdt resize; fdt set /soc@0/pcie@33800000 fsl,max-link-speed [00 00 00 01]'
+saveenv
+}}}
+ * Newport: U-Boot uses a live dt which is also passed to the kernel (dtb is not loaded) so you can alter the dt before running your normal bootscript
+  - Disable PEM2 (PEM0=pci@87e0c0000000, PEM1=pci@87e0c1000000, PEM2=pci@87e0c2000000)
+{{{
+setenv bootscript 'fdt /soc@0/pci@87e0c2000000 status disabled; run distro_bootcmd'
+saveenv
+}}}
+ * Ventana: The {{{loadfdt}}} script will load the dt to the address specified in the {{{fdt_addr}}} env var
+  - disable PCI via {{{fixfdt}}} script:
+{{{
+setenv fixfdt 'fdt addr ${fdt_addr}; fdt resize; fdt set /soc/pcie@0x01000000 status disabled'
+saveenv
+}}}
+
+You can verify your changes took effect by checking the values in Linux via {{{/proc/device-tree}}} or by using {{{dtc}}} to de-compile the dt from {{{/sys/firmware/devicetree/base}}}:
+{{{#!bash
+# de-compile dt via dtc
+dtc -I fs -O dts /sys/firmware/devicetree/base
+# hexdump prop from /proc/device-tree 
+hexdump -C /proc/device-tree/soc\@0/pcie\@33800000/fsl\,max-link-speed
+}}}
+
+=== dt overlay
 Note also that some bootloader environments such as Venice offer dt overlay support where the bootloader can apply overlays to a dt to alter it before passing it to the kernel. In the case of venice you can set the {{{fdt_overlay}}} env variable to a list of files to load and apply as an overlay to modify the base fdt which is typically used for adding features from an add-on board like a display or camera.
 
+See [#overlay below]
 
 == Accessing devicetree from Linux ==
@@ -87 +139 @@
 }}}
 
+
+[=#overlay]
 == Device Tree Overlays (aka Fragments) ==
 The device-tree compiler and the U-Boot bootloader support the concept of applying changes to a base device-tree to make it easy to implement add-on boards such as a touchscreen display or camera that require dt bindings.