IMX Serial Downloader mode detection

[Igor Opaniuk]

Hi,

Currently I'm working on generalizing recovery mode handling,
particularly making sure upon recovery mode (U-boot is loaded via
Serial Downloader) detection the default U-Boot environment is used
rather than the one stored in flash to avoid any bad side-effects.

For the moment we're trying to do that in runtime instead of keeping
two binaries of U-boot, where the first one uses default recovery,
another one uses env from eMMC/NAND.

For iMX8QM/QX Serial Downloader mode detection is done via MU (which
currently exists and workins only in the downstream NXP U-boot fork)
communication with SCFW (sc_misc_get_boot_dev() call etc).

However, for MX6/MX7 series there no any unified way to do so, and the
only way I saw in the downstream NXP U-boot is using some indirect
checks (that don't definetely say that serial download mode was used
to upload this instance of running U-boot) are used, like:
1. Reading value of SRC_SBMR1/SRC_SBMR2
2. Checking for the status of USB OTG PHY, if it was enabled before
U-boot initialed usb stack (is_usbotg_phy_active() from
arch/arm/mach-imx/spl.c NXP U-boot) etc.

The question is: are there any other more proper ways to detect Serial
Download mode?

Thanks

--
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Igor Opaniuk

mailto: igor.opaniuk at gmail.com
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