usb/gadget: add the fastboot gadget

This patch contains an implementation of the fastboot protocol on the
device side and documentation. This is based on USB download gadget
infrastructure. The fastboot function implements the getvar, reboot,
download and reboot commands. What is missing is the flash handling i.e.
writting the image to media.

v3 (Rob Herring):
This is based on http://patchwork.ozlabs.org/patch/126798/ with the
following changes:
- Rebase to current mainline and updates for current gadget API
- Use SPDX identifiers for licenses
- Traced the history and added missing copyright to cmd_fastboot.c
- Use load_addr/load_size for transfer buffer
- Allow vendor strings to be optional
- Set vendor/product ID from config defines
- Allow Ctrl-C to exit fastboot mode
v4:
- Major re-write to use the USB download gadget. Consolidated function
code to a single file.
- Moved globals into single struct.
- Use puts and putc as appropriate.
- Added CONFIG_USB_FASTBOOT_BUF_ADDR and CONFIG_USB_FASTBOOT_BUF_SIZE to
set the fastboot transfer buffer.
v5:
- Add CONFIG option documentation to README
- Rebase using new downloader registration

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Rob Herring <robh@kernel.org>

1 files changed, 170 insertions, 0 deletions

diff --git a/doc/README.android-fastboot-protocol b/doc/README.android-fastboot-protocol
new file mode 100644
index 0000000000..e9e7166a26
--- /dev/null
+++ b/doc/README.android-fastboot-protocol
@@ -0,0 +1,170 @@
+FastBoot  Version  0.4
+----------------------
+
+The fastboot protocol is a mechanism for communicating with bootloaders
+over USB.  It is designed to be very straightforward to implement, to
+allow it to be used across a wide range of devices and from hosts running
+Linux, Windows, or OSX.
+
+
+Basic Requirements
+------------------
+
+* Two bulk endpoints (in, out) are required
+* Max packet size must be 64 bytes for full-speed and 512 bytes for
+  high-speed USB
+* The protocol is entirely host-driven and synchronous (unlike the
+  multi-channel, bi-directional, asynchronous ADB protocol)
+
+
+Transport and Framing
+---------------------
+
+1. Host sends a command, which is an ascii string in a single
+   packet no greater than 64 bytes.
+
+2. Client response with a single packet no greater than 64 bytes.
+   The first four bytes of the response are "OKAY", "FAIL", "DATA",
+   or "INFO".  Additional bytes may contain an (ascii) informative
+   message.
+
+   a. INFO -> the remaining 60 bytes are an informative message
+      (providing progress or diagnostic messages).  They should
+      be displayed and then step #2 repeats
+
+   b. FAIL -> the requested command failed.  The remaining 60 bytes
+      of the response (if present) provide a textual failure message
+      to present to the user.  Stop.
+
+   c. OKAY -> the requested command completed successfully.  Go to #5
+
+   d. DATA -> the requested command is ready for the data phase.
+      A DATA response packet will be 12 bytes long, in the form of
+      DATA00000000 where the 8 digit hexidecimal number represents
+      the total data size to transfer.
+
+3. Data phase.  Depending on the command, the host or client will
+   send the indicated amount of data.  Short packets are always
+   acceptable and zero-length packets are ignored.  This phase continues
+   until the client has sent or received the number of bytes indicated
+   in the "DATA" response above.
+
+4. Client responds with a single packet no greater than 64 bytes.
+   The first four bytes of the response are "OKAY", "FAIL", or "INFO".
+   Similar to #2:
+
+   a. INFO -> display the remaining 60 bytes and return to #4
+
+   b. FAIL -> display the remaining 60 bytes (if present) as a failure
+      reason and consider the command failed.  Stop.
+
+   c. OKAY -> success.  Go to #5
+
+5. Success.  Stop.
+
+
+Example Session
+---------------
+
+Host:    "getvar:version"        request version variable
+
+Client:  "OKAY0.4"               return version "0.4"
+
+Host:    "getvar:nonexistant"    request some undefined variable
+
+Client:  "OKAY"                  return value ""
+
+Host:    "download:00001234"     request to send 0x1234 bytes of data
+
+Client:  "DATA00001234"          ready to accept data
+
+Host:    < 0x1234 bytes >        send data
+
+Client:  "OKAY"                  success
+
+Host:    "flash:bootloader"      request to flash the data to the bootloader
+
+Client:  "INFOerasing flash"     indicate status / progress
+         "INFOwriting flash"
+         "OKAY"                  indicate success
+
+Host:    "powerdown"             send a command
+
+Client:  "FAILunknown command"   indicate failure
+
+
+Command Reference
+-----------------
+
+* Command parameters are indicated by printf-style escape sequences.
+
+* Commands are ascii strings and sent without the quotes (which are
+  for illustration only here) and without a trailing 0 byte.
+
+* Commands that begin with a lowercase letter are reserved for this
+  specification.  OEM-specific commands should not begin with a
+  lowercase letter, to prevent incompatibilities with future specs.
+
+ "getvar:%s"           Read a config/version variable from the bootloader.
+                       The variable contents will be returned after the
+                       OKAY response.
+
+ "download:%08x"       Write data to memory which will be later used
+                       by "boot", "ramdisk", "flash", etc.  The client
+                       will reply with "DATA%08x" if it has enough
+                       space in RAM or "FAIL" if not.  The size of
+                       the download is remembered.
+
+  "verify:%08x"        Send a digital signature to verify the downloaded
+                       data.  Required if the bootloader is "secure"
+                       otherwise "flash" and "boot" will be ignored.
+
+  "flash:%s"           Write the previously downloaded image to the
+                       named partition (if possible).
+
+  "erase:%s"           Erase the indicated partition (clear to 0xFFs)
+
+  "boot"               The previously downloaded data is a boot.img
+                       and should be booted according to the normal
+                       procedure for a boot.img
+
+  "continue"           Continue booting as normal (if possible)
+
+  "reboot"             Reboot the device.
+
+  "reboot-bootloader"  Reboot back into the bootloader.
+                       Useful for upgrade processes that require upgrading
+                       the bootloader and then upgrading other partitions
+                       using the new bootloader.
+
+  "powerdown"          Power off the device.
+
+
+
+Client Variables
+----------------
+
+The "getvar:%s" command is used to read client variables which
+represent various information about the device and the software
+on it.
+
+The various currently defined names are:
+
+  version             Version of FastBoot protocol supported.
+                      It should be "0.3" for this document.
+
+  version-bootloader  Version string for the Bootloader.
+
+  version-baseband    Version string of the Baseband Software
+
+  product             Name of the product
+
+  serialno            Product serial number
+
+  secure              If the value is "yes", this is a secure
+                      bootloader requiring a signature before
+                      it will install or boot images.
+
+Names starting with a lowercase character are reserved by this
+specification.  OEM-specific names should not start with lowercase
+characters.