Re: [PATCH 10/11] ARM: nxp-imx8mq-evk: Add bootflow comments

[Sascha Hauer <s.hauer@pengutronix.de>]

On Fri, Jun 29, 2018 at 08:48:59PM -0700, Andrey Smirnov wrote:
> Add some notes on how the boot-flow goes while I still remember it.
> 
> Signed-off-by: Andrey Smirnov <andrew.smirnov@gmail.com>
> ---
>  arch/arm/boards/nxp-imx8mq-evk/lowlevel.c | 42 +++++++++++++++++++++--
>  1 file changed, 40 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/arm/boards/nxp-imx8mq-evk/lowlevel.c b/arch/arm/boards/nxp-imx8mq-evk/lowlevel.c
> index c2dc6460a..7dd778c21 100644
> --- a/arch/arm/boards/nxp-imx8mq-evk/lowlevel.c
> +++ b/arch/arm/boards/nxp-imx8mq-evk/lowlevel.c
> @@ -66,6 +66,26 @@ static void nxp_imx8mq_evk_sram_setup(void)
>  	BUG_ON(ret);
>  }
>  
> +/*
> + * Power-on execution flow of start_nxp_imx8mq_evk() might not be
> + * obvious for a very frist read, so here's, hopefully helpful,
> + * summary:
> + *
> + * 1. MaskROM uploads PBL into OCRAM and that's where this function is
> + *    executed for the first time
> + *
> + * 2. DDR is initialized and full i.MX image is loaded to the
> + *    beginning of RAM
> + *
> + * 3. start_nxp_imx8mq_evk, now in RAM, is executed again
> + *
> + * 4. BL31 blob is uploaded to OCRAM and the control is transfer to it
> + *
> + * 5. BL31 exits EL3 into EL2 at address MX8MQ_ATF_BL33_BASE_ADDR,
> + *    executing start_nxp_imx8mq_evk() the third time
> + *
> + * 6. Standard barebox boot flow continues
> + */
>  ENTRY_FUNCTION(start_nxp_imx8mq_evk, r0, r1, r2)
>  {
>  	arm_cpu_lowlevel_init();
> @@ -73,11 +93,29 @@ ENTRY_FUNCTION(start_nxp_imx8mq_evk, r0, r1, r2)
>  	if (IS_ENABLED(CONFIG_DEBUG_LL))
>  		setup_uart();
>  
> -	if (get_pc() < MX8MQ_DDR_CSD1_BASE_ADDR)
> +	if (get_pc() < MX8MQ_DDR_CSD1_BASE_ADDR) {
> +		/*
> +		 * We assume that we were just loaded by MaskROM into
> +		 * SRAM if we are not running from DDR. We also assume
> +		 * that means DDR needs to be initialized for the
> +		 * first time.
> +		 */
>  		nxp_imx8mq_evk_sram_setup();
> -
> +	}
> +
> +	/*
> +	 * Straight from the power-on we are at EL3, so the following
> +	 * code _will_ load and jump to ATF.
> +	 *
> +	 * However when this function is re-executed upon exit from
> +	 * ATF's initialization routine, it is EL2 and it is
> +	 * short-circuited to a no-op.
> +	 */
>  	imx8mq_atf_load_bl31(imx_imx8m_bl31_bin);

Maybe the flow would be more clear if we add a if (current_el() == 3)
around the imx8mq_atf_load_bl31()

Sascha

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