[U-Boot] [PATCH v2 2/2] imx_common: detect USB serial downloader reliably

[Eric Nelson]

Hi Stefan,

On 09/08/2017 04:35 PM, Stefan Agner 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>
> Tested-by: Fabio Estevam <fabio.estevam at nxp.com>
> ---
> 
> Changes in v2:
> - Add comment that we infer boot ROM behavior from USB PHY state
> 
>   arch/arm/mach-imx/spl.c | 12 ++++++++++++
>   1 file changed, 12 insertions(+)
> 
> diff --git a/arch/arm/mach-imx/spl.c b/arch/arm/mach-imx/spl.c
> index 258578ac25..f3fec81de7 100644
> --- a/arch/arm/mach-imx/spl.c
> +++ b/arch/arm/mach-imx/spl.c
> @@ -31,6 +31,18 @@ u32 spl_boot_device(void)
>   	if (((bmode >> 24) & 0x03) == 0x01) /* Serial Downloader */
>   		return BOOT_DEVICE_BOARD;
>   
> +	/*
> +	 * The above method does not detect that the boot ROM used
> +	 * serial downloader in case the boot ROM descided to use the
> +	 * serial downloader as a fall back (primary boot source failed).
> +	 *

Nit: should be "did not initialize" instead of "initialized".

Otherwise, this is a nice comment that describes the situation.

> +	 * Infer that the boot ROM used the USB serial downloader by
> +	 * checking whether the USB PHY is currently active... This
> +	 * assumes that SPL did not (yet) initialized the USB PHY...
> +	 */
> +	if (is_usbphy_active())
> +		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 */
>