[U-Boot] [PATCH] ARM: mxs: spl_boot.c: make early_delay more robust

[Fabio Estevam]

[Adding Marek]

On Tue, Sep 10, 2019 at 5:32 AM Rasmus Villemoes
<rasmus.villemoes at prevas.dk> wrote:
>
> It's true that booting normally doesn't take long enough for the
> register to roll (which actually happens in a little over an hour, not
> just a few seconds). However, the counter starts at power-on, and if
> the board is held in reset to be booted over USB, one actually risks
> hitting wrap-around during boot, which can both result in too short
> delays (if the "st += delay" calculation makes st small) and
> theoretically also unbound delays (if st ends up being UINT_MAX and
> one just misses sampling digctl_microseconds at that point).
>
> It doesn't take more code to DTRT, and once bitten, twice shy.
>
> Signed-off-by: Rasmus Villemoes <rasmus.villemoes at prevas.dk>
> ---
>  arch/arm/cpu/arm926ejs/mxs/spl_boot.c | 7 ++-----
>  1 file changed, 2 insertions(+), 5 deletions(-)
>
> diff --git a/arch/arm/cpu/arm926ejs/mxs/spl_boot.c b/arch/arm/cpu/arm926ejs/mxs/spl_boot.c
> index cb361ac65c..336266fe82 100644
> --- a/arch/arm/cpu/arm926ejs/mxs/spl_boot.c
> +++ b/arch/arm/cpu/arm926ejs/mxs/spl_boot.c
> @@ -24,9 +24,7 @@ static bd_t bdata __section(".data");
>
>  /*
>   * This delay function is intended to be used only in early stage of boot, where
> - * clock are not set up yet. The timer used here is reset on every boot and
> - * takes a few seconds to roll. The boot doesn't take that long, so to keep the
> - * code simple, it doesn't take rolling into consideration.
> + * clock are not set up yet.
>   */
>  void early_delay(int delay)
>  {
> @@ -34,8 +32,7 @@ void early_delay(int delay)
>                 (struct mxs_digctl_regs *)MXS_DIGCTL_BASE;
>
>         uint32_t st = readl(&digctl_regs->hw_digctl_microseconds);
> -       st += delay;
> -       while (st > readl(&digctl_regs->hw_digctl_microseconds))
> +       while (readl(&digctl_regs->hw_digctl_microseconds) - st <= delay)
>                 ;

Looks reasonable for me.

Thanks