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>

arch/arm/imx-common/spl.c

@@ -20,7 +20,15 @@ u32 spl_boot_device(void)
 	struct src *psrc = (struct src *)SRC_BASE_ADDR;
 	unsigned int gpr10_boot = readl(&psrc->gpr10) & (1 << 28);
 	unsigned reg = gpr10_boot ? readl(&psrc->gpr9) : readl(&psrc->sbmr1);
+	unsigned int bmode = readl(&psrc->sbmr2);
 
+	/*
+	 * Check for BMODE if serial downloader is enabled
+	 * BOOT_MODE - see IMX6DQRM Table 8-1
+	 */
+	if ((((bmode >> 24) & 0x03)  == 0x01) || /* Serial Downloader */
+		(gpr10_boot && (reg == 1)))
+		return BOOT_DEVICE_UART;
 	/* BOOT_CFG1[7:4] - see IMX6DQRM Table 8-8 */
 	switch ((reg & 0x000000FF) >> 4) {
 	 /* EIM: See 8.5.1, Table 8-9 */

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.