[U-Boot] [PATCH v1 2/2] imx_common: detect USB serial downloader reliably

[Stefan Agner]

From: Stefan Agner <stefan.agner at toradex.com>

The current mechanism using SCR/GPR registers work well when
the serial downloader boot mode has been selected explicitly
(either via boot mode pins or using bmode command). However,
in case the system entered boot ROM due to unbootable primary
boot devices (e.g. empty eMMC), the SPL fails to detect that
it has been downloaded through serial loader and tries to
continue booting from eMMC:
  Trying to boot from MMC1
  mmc_load_image_raw_sector: mmc block read error
  SPL: failed to boot from all boot devices
  ### ERROR ### Please RESET the board ###

The only known way to reliably detect USB serial downloader
is by checking the USB PHY receiver block power state...

Signed-off-by: Stefan Agner <stefan.agner at toradex.com>
Acked-by: Marcel Ziswiler <marcel.ziswiler at toradex.com>
---

 arch/arm/mach-imx/spl.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/arch/arm/mach-imx/spl.c b/arch/arm/mach-imx/spl.c
index 258578ac25..8e8e2f755b 100644
--- a/arch/arm/mach-imx/spl.c
+++ b/arch/arm/mach-imx/spl.c
@@ -31,6 +31,10 @@ u32 spl_boot_device(void)
 	if (((bmode >> 24) & 0x03) == 0x01) /* Serial Downloader */
 		return BOOT_DEVICE_BOARD;
 
+	/* Check USB state in case we entered serial downloader as fallback */
+	if (is_boot_from_usb())
+		return BOOT_DEVICE_BOARD;
+
 	/* BOOT_CFG1[7:4] - see IMX6DQRM Table 8-8 */
 	switch ((reg & IMX6_BMODE_MASK) >> IMX6_BMODE_SHIFT) {
 	 /* EIM: See 8.5.1, Table 8-9 */
-- 
2.14.1