[PATCH v4 7/8] doc: uefi: add HTTP Boot support

[Masahisa Kojima]

This adds the description about HTTP Boot.

Signed-off-by: Masahisa Kojima <masahisa.kojima at linaro.org>
---
 doc/develop/uefi/uefi.rst | 30 ++++++++++++++++++++++++++++++
 1 file changed, 30 insertions(+)

diff --git a/doc/develop/uefi/uefi.rst b/doc/develop/uefi/uefi.rst
index a7a41f2fac..65eea89265 100644
--- a/doc/develop/uefi/uefi.rst
+++ b/doc/develop/uefi/uefi.rst
@@ -594,6 +594,36 @@ UEFI variables. Booting according to these variables is possible via::
 As of U-Boot v2020.10 UEFI variables cannot be set at runtime. The U-Boot
 command 'efidebug' can be used to set the variables.
 
+UEFI HTTP Boot
+~~~~~~~~~~~~~~
+
+HTTP Boot provides the capability for system deployment and configuration
+over the network. HTTP Boot can be activated by specifying::
+
+    CONFIG_CMD_DNS
+    CONFIG_CMD_WGET
+    CONFIG_BLKMAP
+
+Set up the load option specifying the target URI::
+
+    efidebug boot add -u 1 netinst http://foo/bar
+
+When this load option is selected as boot selection, resolve the
+host ip address by dns, then download the file with wget.
+If the downloaded file extension is .iso or .img file, efibootmgr tries to
+mount the image and boot with the default file(e.g. EFI/BOOT/BOOTAA64.EFI).
+If the downloaded file is PE-COFF image, load the downloaded file and
+start it.
+
+There is a limitation that current implementation tries to resolve
+the IP address as a host name. If the uri is like "http://192.168.1.1/foobar",
+the dns process tries to resolve the host "192.168.1.1" and it will
+end up with "host not found".
+
+We need to preset the "httpserverip" environment variable to proceed the wget::
+
+    setenv httpserverip 192.168.1.1
+
 Executing the built in hello world application
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
-- 
2.34.1