imx_common: check for Serial Downloader in spl_boot_device

Check for bmode before reading the boot device
to check if a serial downloader is started,
and returns UART if the serial downloader is set,
letting SPL to wait for an image if
CONFIG_SPL_YMODEM_SUPPORT is set.

This allows to load again a SPL based board
with imx_usb_loader together with a tool
such as kermit.

Signed-off-by: Stefano Babic <sbabic@denx.de>
CC: Tim Harvey <tharvey@gateworks.com>
CC: Fabio Estevam <Fabio.Estevam@freescale.com>
CC: Eric Nelson <eric.nelson@boundarydevices.com>
Reviewed-by: Eric Nelson <eric@nelint.com>
Tested-by: Eric Nelson <eric@nelint.com>

1 files changed, 51 insertions, 0 deletions

diff --git a/doc/README.imx6 b/doc/README.imx6
index 437af2f..e26ab71 100644
--- a/doc/README.imx6
+++ b/doc/README.imx6
@@ -84,3 +84,54 @@ Address:
 Reading bank 4:
 
 Word 0x00000002: 9f027772 00000004
+
+2. Using imx_usb_loader for first install with SPL
+--------------------------------------------------
+
+imx_usb_loader is a very nice tool by BoundaryDevice that
+allow to install U-Boot without a JTAG debugger, using
+the USB boot mode as described in the manual. It is
+a replacement for Freescale's MFGTOOLS.
+
+The sources can be found here:
+
+	https://github.com/boundarydevices/imx_usb_loader.git
+
+Booting in USB mode, the i.MX6 announces itself to the Linux Host as:
+
+Bus 001 Device 111: ID 15a2:0061 Freescale Semiconductor, Inc.
+
+imx_usb_loader is able to download a single file (u-boot.imx)
+to the board. For boards without SPL support, it is enough to
+issue the command:
+
+	sudo ../imx_usb_loader/imx_usb -v u-boot.imx
+
+Getting U-Boot when SPL support is active, it requires
+two downloads. imx_usb_loader downloads the SPL into
+OCRAM and starts it. SPL will check for a valid u-boot.img, and
+because it is not found, it will wait for it using the y-modem
+protocol via the console.
+
+A first install is then possible by combining imx_usb_loader with
+another tool such as kermit.
+
+sudo ../imx_usb_loader/imx_usb -v SPL
+kermit kermit_uboot
+
+and kermit_uboot contains something like this (set line should be adjusted):
+
+set line /dev/ttyUSB1
+set speed 115200
+SET CARRIER-WATCH OFF
+set flow-control none
+set handshake none
+set prefixing all
+set file type bin
+set protocol ymodem
+send u-boot.img
+c
+
+The last "c" command tells kermit (from ckermit package in most distros)
+to switch from command line mode to communication mode, and when the
+script is finished, the U-Boot prompt is shown in the same shell.