[PATCH v3 6/6] board: samsung: e850-96: Enter DFU automatically on USB boot

[Sam Protsenko]

Doing USB boot on E850-96 is most useful in two cases:

  1. For unbricking the board
  2. During the bootloader development

In both cases a U-Boot binary is being re-flashed to eMMC. The most
convenient way to update U-Boot in eMMC is by using DFU. Implement
entering DFU flashing mode automatically when U-Boot is executed on USB
boot. That makes it easier for users to re-flash U-Boot without even
having serial console running, e.g.:

    $ ./smdk-usbdl
    $ dfu-util -D u-boot.bin -a bootloader

See [1,2] for details.

Entering DFU mode is implemented by setting corresponding environment
variables:

    bootcmd="dfu 0 mmc 0"
    bootdelay=0

Do not save the U-Boot environment though, to avoid falling through to
DFU mode on a regular eMMC boot.

[1] doc/board/samsung/e850-96.rst
[2] https://gitlab.com/LinaroLtd/e850-96/tools/dltool/-/tree/uboot

Signed-off-by: Sam Protsenko <semen.protsenko at linaro.org>
---
Changes in v3:
  - This patch is added in v3

 board/samsung/e850-96/e850-96.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/board/samsung/e850-96/e850-96.c b/board/samsung/e850-96/e850-96.c
index 3aa4992a36d5..415505f2561c 100644
--- a/board/samsung/e850-96/e850-96.c
+++ b/board/samsung/e850-96/e850-96.c
@@ -209,6 +209,12 @@ int board_late_init(void)
 	else
 		load_firmware_blk();
 
+	if (bootdev_is_usb()) {
+		env_set("bootcmd", "echo \"Entering DFU mode...\"; "
+			"dfu 0 mmc 0");
+		env_set("bootdelay", "0");
+	}
+
 	return 0;
 }
 
-- 
2.47.3