add README.md

Change-Id: I65feab3957dea0ae7c246f4fb9cc0bae82297d20
Signed-off-by: Cedric Chaumont <[email protected]>

README.md

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+# OP-TEE Trusted OS
+The optee_os git, containing the source code for the TEE in Linux using
+the ARM(R) Trustzone(R) technology. This component meets the Global
+Platform TEE System Architecture specification. It also provides the
+TEE Internal API v1.0 as defined by the Global Platform TEE Standard
+for the development of trusted apllications.
+It is distributed mostly under the BSD 2-clause open-source license.
+It includes few external files under BSD 3-clause license or other free
+software licenses. For a general overview of OP-TEE, please see the
+[Notice.md](Notice.md) file.
+
+In this git, the binary to build is tee.elf.
+The Trusted OS is accessible from the Rich OS (Linux) through the Global
+Platform TEE Client API and performs secure execution of applications
+inside the TEE.
+
+## License
+The software is provided under the
+[BSD 2-Clause](http://opensource.org/licenses/BSD-2-Clause) license.
+[BSD 3-Clause](http://opensource.org/licenses/BSD-3-Clause) license.
+
+## Platforms supported
+This software has hardware dependencies.
+The software has been tested using:
+
+- STMicroelectronics b2020-h416 (orly-2) hardware (32-bits)
+- Some initial testing has been done using
+[Foundation FVP](http://www.arm.com/fvp), which can be downloaded free of
+charge.
+
+## Get and build the software
+### Get the compiler
+We will strive to use the latest available compiler from Linaro. Start by
+downloading and unpacking the compiler. Then export the PATH to the bin folder.
+
+	$ cd $HOME
+	$ mkdir toolchains
+	$ cd toolchains
+	$ wget http://releases.linaro.org/14.05/components/toolchain/binaries/gcc-linaro-arm-linux-gnueabihf-4.9-2014.05_linux.tar.xz
+	$ tar xvf gcc-linaro-arm-linux-gnueabihf-4.9-2014.05_linux.tar.xz
+	$ export PATH=$HOME/toolchains/gcc-linaro-arm-linux-gnueabihf-4.9-2014.05_linux/bin:$PATH
+
+### Download the source code
+	$ cd $HOME
+	$ mkdir devel
+	$ cd devel
+	$ git clone https://github.com/OP-TEE/optee_os.git
+
+### Build
+	$ cd $HOME/devel/optee_os
+	$ CROSS_COMPILE=arm-linux-gnueabihf- make
+
+#### Compiler flags
+To be able to see the full command when building you could build using following
+flag:
+
+`$ make V=1`
+
+## Coding standards
+In this project we are trying to adhere to the same coding convention as used in
+the Linux kernel (see
+[CodingStyle](https://www.kernel.org/doc/Documentation/CodingStyle)). We achieve this by running
+[checkpatch](http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/scripts/checkpatch.pl) from Linux kernel.
+However there are a few exceptions that we had to make since the code also
+follows GlobalPlatform standards. The exceptions are as follows:
+
+- CamelCase for GlobalPlatform types are allowed.
+- And we also exclude checking third party code that we might use in this
+  project, such as LibTomCrypt, MPA, newlib (not in this particular git, but
+  those are also part of the complete TEE solution). The reason for excluding
+  and not fixing third party code is because we would probably deviate too much
+  from upstream and therefore it would be hard to rebase against those projects
+  later on (and we don't expect that it is easy to convince other software
+  projects to change coding style).
+
+### checkpatch
+Since checkpatch is licensed under the terms of GNU GPL License Version 2, we
+cannot include this script directly into this project. Therefore we have
+written the Makefile so you need to explicitly point to the script by exporting
+an environment variable, namely CHECKPATCH. So, suppose that the source code for
+the Linux kernel is at `$HOME/devel/linux`, then you have to export like follows:
+
+	$ export CHECKPATCH=$HOME/devel/linux/scripts/checkpatch.pl
+thereafter it should be possible to use one of the different checkpatch targets
+in the [Makefile](Makefile). There are targets for checking all files, checking
+against latest commit, against a certain base-commit etc. For the details, read
+the [Makefile](Makefile).