lib: Add devtree_update bootstate hook

Provide a weak devtree_update() hook and invoke it early in ramstage
at BS_PRE_DEVICE. Mainboards can override devtree_update() to
enable/disable devices at runtime based on CMOS/NVRAM settings.

Signed-off-by: Sean Rhodes <sean@starlabs.systems>
Change-Id: Ic84ddb25e1da050543c230ea457042b8a8a3061f
Reviewed-on: https://review.coreboot.org/c/coreboot/+/91250
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Matt DeVillier <matt.devillier@gmail.com>
Reviewed-by: Angel Pons <th3fanbus@gmail.com>

src/include/devtree_update.h

@@ -0,0 +1,14 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+
+#ifndef __DEVTREE_UPDATE_H__
+#define __DEVTREE_UPDATE_H__
+
+/*
+ * Optional mainboard hook to update devicetree runtime enable/disable state
+ * based on CMOS/NVRAM settings.
+ *
+ * This function is called early in ramstage at BS_PRE_DEVICE.
+ */
+void devtree_update(void);
+
+#endif /* __DEVTREE_UPDATE_H__ */

src/lib/Makefile.mk

@@ -155,6 +155,7 @@ ramstage-$(CONFIG_BOOTSPLASH) += bootsplash.c
 ramstage-$(CONFIG_BOOTSPLASH) += jpeg.c
 ramstage-$(CONFIG_COLLECT_TIMESTAMPS) += timestamp.c
 ramstage-$(CONFIG_COVERAGE) += libgcov.c
+ramstage-y += devtree_update.c
 ramstage-y += dp_aux.c
 ramstage-y += framebuffer_info.c
 ramstage-y += edid.c

src/lib/devtree_update.c

@@ -0,0 +1,16 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+
+#include <bootstate.h>
+#include <commonlib/bsd/compiler.h>
+#include <devtree_update.h>
+
+__weak void devtree_update(void)
+{
+}
+
+static void run_devtree_update(void *unused)
+{
+	devtree_update();
+}
+
+BOOT_STATE_INIT_ENTRY(BS_PRE_DEVICE, BS_ON_ENTRY, run_devtree_update, NULL);