Add content about support system_dlkm partition

Bug: 256984997
Test: n/a
Change-Id: I25cd380e7bd04d7b068147d29def6a67602beac3

1 files changed, 30 insertions, 1 deletions

diff --git a/README.md b/README.md
index 0938785..fcb14e6 100644
--- a/README.md
+++ b/README.md
@@ -3,7 +3,36 @@
 This document introduces special GSI settings for facilitating xTS-on-GSI with
 a single image.
 
-## Changes in runtime resource overlays (RRO)
+### Support system_dlkm partition
+
+```
+[BoardConfigGsiCommon.mk]
+
+BOARD_USES_SYSTEM_DLKMIMAGE := true
+BOARD_SYSTEM_DLKMIMAGE_FILE_SYSTEM_TYPE := ext4
+TARGET_COPY_OUT_SYSTEM_DLKM := system_dlkm
+
+[gsi_release.mk]
+
+PRODUCT_BUILD_SYSTEM_DLKM_IMAGE := false
+```
+
+Starting from Android 13, all devices must include a [system_dlkm partition].
+GSI enables system_dlkm to support the devices with system_dlkm partition,
+and be compatible with old devices without a system_dlkm partition.
+
+With these configurations, `/system/system_dlkm` would not be created.
+Instead, a `/system/lib/modules` -> `/system_dlkm/lib/modules` symlink is
+created.
+
+For device without system_dlkm partition, the symlink would be dangling.
+The dangling symlink shouldn't be followed anyway because the device doesn't
+use system_dlkm.
+
+For device with system_dlkm, they can load modules via that path normally like
+when they are using their original system image.
+
+[system_dlkm partition]: https://source.android.com/docs/core/architecture/bootloader/partitions/gki-partitions
 
 ### SystemUI overlays