Reset on Beaglebone Black has become unreliable/broken

[Ahmad Fatoum]

Hello Konstantin,

On 20.12.24 12:05, Konstantin Kletschke wrote:
> I found the minimum change required to make barebox warm restart every
> time I hot S1, write warm restart register, type reset or linux kernel
> reboot.
> I needed to figure out to realize in my yocto the MLO stage is another
> package to test my changes in this vanilla defconfig part carefully.
> 
> My barebox-pbl stage package calls the defconfig am335x_mlo_defconfig, I
> apply only this patch on top on my 2022.04 version:

Thanks for the follow-up.

> diff --git a/arch/arm/boards/beaglebone/lowlevel.c b/arch/arm/boards/beaglebone/lowlevel.c
> index 544e396e03..329d7a9150 100644
> --- a/arch/arm/boards/beaglebone/lowlevel.c
> +++ b/arch/arm/boards/beaglebone/lowlevel.c
> @@ -97,6 +97,12 @@ extern char __dtb_z_am335x_boneblack_start[];
>  extern char __dtb_z_am335x_bone_common_start[];
>  extern char __dtb_z_am335x_bone_start[];
> 
> +static void __udelay(int us)
> +{
> +	volatile int i;
> +	for (i = 0; i < us * 3; i++);
> +}
> +
>  /**
>   * @brief The basic entry point for board initialization.
>   *
> @@ -142,6 +148,7 @@ static noinline int beaglebone_sram_init(void)
>  	omap_uart_lowlevel_init((void *)AM33XX_UART0_BASE);
>  	putc_ll('>');
> 
> +	__udelay(1000);
>  	barebox_arm_entry(0x80000000, sdram_size, fdt);
>  }
> 
> 
> This delay loop (side quest: how do I calculate how long it waits?)

Try multiplying it by 1 000 or 1 000 000 and print a character before
and after and measure this time difference, e.g. with grabserial[0]
or ts(1) and then divide by the factor you first used for multiplication.

[0]: https://elinux.org/Grabserial

> on its own with no changes in CONFIG or debugging or whatsoever
> fixes everything.

If it's indeed just a millisecond, I am in favor of adding this to
barebox upstream with a comment explaining what this fixes, even
if we don't fully understand it yet.

Cheers,
Ahmad

> 
> Regards
> Konstantin
> 


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