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Yifan Hong 2018-10-16 11:00:35 -07:00
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@ -1,15 +1,13 @@
Android Kernel Configs
======================
# Android Kernel Configs
How are kernel config settings typically stored?
------------------------------------------------
## How are kernel config settings typically stored?
When building the Linux kernel for a particular platform one usually begins by
basing the kernel configuration off of a particular defconfig. The platform’s
defconfig contains all of the Linux kconfig settings required to properly
configure the kernel build (features, default system parameters, etc) for that
platform. Defconfig files are typically stored in the kernel tree at
arch/*/configs/.
`arch/*/configs/`.
It may be desirable to modify the kernel configuration beyond what the hardware
platform requires in order to support a particular hardware or software
@ -22,8 +20,7 @@ compactly express their kernel requirements. The fragments can be combined
with a platform defconfig using the kernel's make rules or using the
`scripts/kconfig/merge_config.sh` script in the kernel tree.
How are Android's kernel configs stored?
----------------------------------------
## How are Android's kernel configs stored?
The kernel configs are stored in the [kernel/configs repo](https://android.googlesource.com/kernel/configs/).
@ -44,15 +41,14 @@ apply in that case.
Kernel configs vary by kernel version, so there are sets of kernel configs for
each version of the kernel that Android supports.
How can I easily combine platform and required Android configs?
---------------------------------------------------------------
## How can I easily combine platform and required Android configs?
Assuming you already have a minimalist defconfig for your platform, a possible
way to enable these options would be to use the aforementioned
`merge_config.sh` script in the kernel tree. From the root of the kernel tree:
```sh
ARCH=<arch> scripts/kconfig/merge_config.sh <...>/<platform>_defconfig <...>/android-base.config <...>/android-base-<arch>.config <...>/android-recommended.config
ARCH=<arch> scripts/kconfig/merge_config.sh <...>/<platform>_defconfig <...>/android-base.config <...>/android-base-<arch>.config <...>/android-recommended.config
```
This will generate a `.config` that can then be used to save a new defconfig or
@ -64,12 +60,11 @@ and they must have filenames that end with the extension ".config". The
platform defconfig must also be located in `arch/<arch>/configs/`. Once these
requirements are satisfied, the full defconfig can be prepared with:
```
```sh
make ARCH=<arch> <platform>_defconfig android-base.config android-base-<arch>.config android-recommended.config
```
Are the config requirements tested?
-------------------------------------
## Are the config requirements tested?
Starting with Android O the base kernel configs are not just advisory. They
are tested as part of VTS in the
@ -77,8 +72,7 @@ are tested as part of VTS in the
test, and also during device boot when the vendor interface (which includes the
kernel configuration) and framework compatibility matrix are compared.
Ensuring Device Upgradability
-----------------------------
## Ensuring Device Upgradability
Devices launched with prior releases of Android must be able to upgrade to
later releases of Android. This means that AOSP must function not only with
@ -100,8 +94,7 @@ upgrade path are in the kernel/configs repo.
Support for kernel configs from previous dessert releases is dropped from AOSP
when the upgrade path from that dessert release is no longer supported.
Organization and Maintenance of the Kernel Config Repo
------------------------------------------------------
# Organization and Maintenance of the Kernel Config Repo
The top level of the kernel configs repo contains directories for each
supported kernel version. These contain the kernel config requirements (and
@ -117,8 +110,7 @@ copied into a new directory for the release (this change is propagated to
master) and the top-level configs are removed (this change is not propagated to
master) since no development beyond that release is done in that branch.
I want to add/modify/remove a kernel config requirement. What do I do?
-----------------------------------------------------------------------------
## I want to add/modify/remove a kernel config requirement. What do I do?
Modify the top level kernel configs in AOSP. Make sure to modify the configs
for all applicable kernel versions. Do not modify the config fragments in