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

[Fabio Estevam]

On Mon, Sep 4, 2017 at 10:21 PM, Stefan Agner <stefan at agner.ch> wrote:
> 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>

This allows Serial Download Protocol to work on imx6q sabresd:

Tested-by: Fabio Estevam <fabio.estevam at nxp.com>