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

[Simon Glass]

Hi Bin,

On 25 September 2018 at 23:39, Bin Meng <bmeng.cn at gmail.com> wrote:
> Hi Simon,
>
> On Wed, Sep 26, 2018 at 1:42 PM Simon Glass <sjg at chromium.org> wrote:
>>
>> Hi Bin,
>>
>> On 4 September 2018 at 03:06, Bin Meng <bmeng.cn at gmail.com> wrote:
>> > 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
>>
>> Well we could, but I suspect that would break things since the early
>> timer is not supported by many boards. Also for most boards this
>> doesn't actually work fine. x86 is really quite awful in that it has
>> no SRAM and the CAR becomes inaccessible as soon as you turn on the
>> cache!
>
> It's true that early timer is supported by some limited boards, but
> that's a different issue. For now that patch does not fix anything. If
> we add BOOTSTAGE from either defconfig or 'menuconfig' for a board,
> without adding TIMER_EARLY, it will for sure break.

Is this because of code called in board_f.c ? I don't quite follow.

Regards,
Simon