[U-Boot] [PATCH 1/4] Enable CONFIG_TIMER_EARLY with bootstage

[Bin Meng]

Hi Simon,

On Mon, Sep 3, 2018 at 7:02 AM Simon Glass <sjg at chromium.org> wrote:
>
> In initr_bootstage() we call bootstage_mark_name() which ends up calling
> timer_get_us(). This call happens before initr_dm(), which inits driver
> model.
>
> On x86 we set gd->timer to NULL in the transition from board_init_f()

It's not just x86 we set gd->timer to NULL. It applied to all
architectures when CONFIG_TIMER is on.

> to board_init_r(). See board_init_f_r() for this assignment. So U-Boot
> knows there is no timer available in the period immediately after
> relocation.
>
> On x86 the timer_get_us() call is implemented as calls to get_ticks() and
> get_tbclk(). Both of these call dm_timer_init() to set up the timer, if
> gd->timer is NULL and the early timer is not available.
>
> However dm_timer_init() cannot succeed before initr_dm() is called.
>
> So it seems that on x86 if we want to use CONFIG_BOOTSTAGE we must enable
> CONFIG_TIMER_EARLY. Update the Kconfig to handle this.
>
> Note: On most architectures we can rely on the pre-relocation memory still
> being available, so that gd->timer pointers to a valid timer device and
> everything works correctly. Admittedly this is not strictly correct since
> the timer device is set up by pre-relocation U-Boot, but normally this is
> fine. On x86 the 'CAR' (cache-as-RAM) memory used by pre-relocation U-Boot
> disappears in board_init_f_r() and any attempt to access it will hang.
> This is the reason why we must mark the timer as invalid when we get to
> board_init_f_r().
>
> Signed-off-by: Simon Glass <sjg at chromium.org>
> ---
>
>  drivers/timer/Kconfig | 3 +++
>  1 file changed, 3 insertions(+)
>
> diff --git a/drivers/timer/Kconfig b/drivers/timer/Kconfig
> index 5ab6749193c..ff434de6f7c 100644
> --- a/drivers/timer/Kconfig
> +++ b/drivers/timer/Kconfig
> @@ -30,6 +30,9 @@ config TPL_TIMER
>  config TIMER_EARLY
>         bool "Allow timer to be used early in U-Boot"
>         depends on TIMER
> +       # initr_bootstage() requires a timer and is called before initr_dm()
> +       # so only the early timer is available
> +       default y if X86 && BOOTSTAGE

Since this applies not only on x86, and given without TIMER_EARLY
BOOTSTAGE is broken, shouldn't we do this in BOOTSTAGE config instead:

config BOOTSTAGE
         select TIMER_EARLY

>         help
>           In some cases the timer must be accessible before driver model is
>           active. Examples include when using CONFIG_TRACE to trace U-Boot's
> --

Regards,
Bin