hw/arm/imx8mp-evk: Remove unimplemented cpu-idle-states properties from devicetree

The cpu-idle-states property causes a hard boot hang. Rather than documenting
the workaround, perform the removal from the devicetree automatically.

Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Bernhard Beschow <shentey@gmail.com>
[Bernhard: split patch, update documentation, adapt commit message]
Signed-off-by: Bernhard Beschow <shentey@gmail.com>
Message-ID: <20250405214900.7114-3-shentey@gmail.com>
Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>

docs/system/arm/imx8mp-evk.rst

@@ -35,7 +35,7 @@ Direct Linux Kernel Boot
 
 Probably the easiest way to get started with a whole Linux system on the machine
 is to generate an image with Buildroot. Version 2024.11.1 is tested at the time
-of writing and involves three steps. First run the following commands in the
+of writing and involves two steps. First run the following commands in the
 toplevel directory of the Buildroot source tree:
 
 .. code-block:: bash
@@ -50,14 +50,6 @@ it and resize the SD card image to a power of two:
 
   $ qemu-img resize sdcard.img 256M
 
-Finally, the device tree needs to be patched with the following commands which
-will remove the ``cpu-idle-states`` properties from CPU nodes:
-
-.. code-block:: bash
-
-  $ dtc imx8mp-evk.dtb | sed '/cpu-idle-states/d' > imx8mp-evk-patched.dts
-  $ dtc imx8mp-evk-patched.dts -o imx8mp-evk-patched.dtb
-
 Now that everything is prepared the machine can be started as follows:
 
 .. code-block:: bash
@@ -65,6 +57,6 @@ Now that everything is prepared the machine can be started as follows:
   $ qemu-system-aarch64 -M imx8mp-evk -smp 4 -m 3G \
       -display none -serial null -serial stdio \
       -kernel Image \
-      -dtb imx8mp-evk-patched.dtb \
+      -dtb imx8mp-evk.dtb \
       -append "root=/dev/mmcblk2p2" \
       -drive file=sdcard.img,if=sd,bus=2,format=raw,id=mmcblk2

hw/arm/imx8mp-evk.c

@@ -15,6 +15,19 @@
 #include "system/qtest.h"
 #include "qemu/error-report.h"
 #include "qapi/error.h"
+#include <libfdt.h>
+
+static void imx8mp_evk_modify_dtb(const struct arm_boot_info *info, void *fdt)
+{
+    int offset;
+
+    /* Remove cpu-idle-states property from CPU nodes */
+    offset = fdt_node_offset_by_compatible(fdt, -1, "arm,cortex-a53");
+    while (offset >= 0) {
+        fdt_nop_property(fdt, offset, "cpu-idle-states");
+        offset = fdt_node_offset_by_compatible(fdt, offset, "arm,cortex-a53");
+    }
+}
 
 static void imx8mp_evk_init(MachineState *machine)
 {
@@ -32,6 +45,7 @@ static void imx8mp_evk_init(MachineState *machine)
         .board_id = -1,
         .ram_size = machine->ram_size,
         .psci_conduit = QEMU_PSCI_CONDUIT_SMC,
+        .modify_dtb = imx8mp_evk_modify_dtb,
     };
 
     s = FSL_IMX8MP(object_new(TYPE_FSL_IMX8MP));