efi: Update README.efi to clarify build and test instructions

The doc has a misleading 'make menuconfig' when building the EFI
application and payload. Clarify this and also update information
on test with QEMU.

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
Acked-by: Simon Glass <sjg@chromium.org>

doc/README.efi

@@ -47,23 +47,25 @@ machine. You can use devices, boot a kernel, etc.
 Build Instructions
 ------------------
 First choose a board that has EFI support and obtain an EFI implementation
-for that board. It will be either 32-bit or 64-bit.
+for that board. It will be either 32-bit or 64-bit. Alternatively, you can
+opt for using QEMU [1] and the OVMF [2], as detailed below.
 
-To build U-Boot as an EFI application (32-bit EFI required), enable
-CONFIG_EFI and CONFIG_EFI_APP. The efi-x86 config is set up for this.
+To build U-Boot as an EFI application (32-bit EFI required), enable CONFIG_EFI
+and CONFIG_EFI_APP. The efi-x86 config (efi-x86_defconfig) is set up for this.
+Just build U-Boot as normal, e.g.
 
-To build U-Boot as an EFI payload (32-bit or 64-bit EFI can be used), adjust
-an existing config to enable CONFIG_EFI, CONFIG_EFI_STUB and either
-CONFIG_EFI_STUB_32BIT or CONFIG_EFI_STUB_64BIT.
+   make efi-x86_defconfig
+   make
 
-Then build U-Boot as normal, e.g.
+To build U-Boot as an EFI payload (32-bit or 64-bit EFI can be used), adjust an
+existing config (like qemu-x86_defconfig) to enable CONFIG_EFI, CONFIG_EFI_STUB
+and either CONFIG_EFI_STUB_32BIT or CONFIG_EFI_STUB_64BIT. All of these are
+boolean Kconfig options. Then build U-Boot as normal, e.g.
 
    make qemu-x86_defconfig
-   make menuconfig    (or make xconfig if you prefer)
-   # change the settings as above
    make
 
-You will end up with one of these files:
+You will end up with one of these files depending on what you build for:
 
    u-boot-app.efi      - U-Boot EFI application
    u-boot-payload.efi  - U-Boot EFI payload application
@@ -71,8 +73,9 @@ You will end up with one of these files:
 
 Trying it out
 -------------
-Qemu is an emulator and it can emulate an x86 machine. You can run the
-payload with something like this:
+QEMU is an emulator and it can emulate an x86 machine. Please make sure your
+QEMU version is 2.3.0 or above to test this. You can run the payload with
+something like this:
 
    mkdir /tmp/efi
    cp /path/to/u-boot*.efi /tmp/efi
@@ -80,7 +83,8 @@ payload with something like this:
 
 Add -nographic if you want to use the terminal for output. Once it starts
 type 'fs0:u-boot-payload.efi' to run the payload or 'fs0:u-boot-app.efi' to
-run the application. 'bios.bin' is the EFI 'BIOS'.
+run the application. 'bios.bin' is the EFI 'BIOS'. Check [2] to obtain a
+prebuilt EFI BIOS for QEMU or you can build one from source as well.
 
 To try it on real hardware, put u-boot-app.efi on a suitable boot medium,
 such as a USB stick. Then you can type something like this to start it:
@@ -235,3 +239,6 @@ common/cmd_efi.c
 Ben Stoltz, Simon Glass
 Google, Inc
 July 2015
+
+[1] http://www.qemu.org
+[2] http://www.tianocore.org/ovmf/