Re: [PATCH 2/6] timer: orion-timer: Add timer_get_boot_us() for BOOTSTAGE support

Stefan Roese
2022-08-31T05:57:10Z

Hi Simon,

On 30.08.22 17:56, Simon Glass wrote:
> Hi Stefan,
>
> On Tue, 30 Aug 2022 at 06:08, Stefan Roese <sr@denx.de> wrote:
>>
>> Adding Simon to Cc...
>>
>> On 30.08.22 14:00, Michael Walle wrote:
>>> Am 2022-08-30 13:53, schrieb Stefan Roese:
>>>> Add timer_get_boot_us() to support boards, that have CONFIG_BOOTSTAGE
>>>> enabled, like pogo_v4.
>>>>
>>>> Signed-off-by: Stefan Roese <sr@denx.de>
>>>> ---
>>>> drivers/timer/orion-timer.c | 22 ++++++++++++++++++++++
>>>> 1 file changed, 22 insertions(+)
>>>>
>>>> diff --git a/drivers/timer/orion-timer.c b/drivers/timer/orion-timer.c
>>>> index 02ed138642b8..7e920eaeaa40 100644
>>>> --- a/drivers/timer/orion-timer.c
>>>> +++ b/drivers/timer/orion-timer.c
>>>> @@ -41,6 +41,28 @@ u64 notrace timer_early_get_count(void)
>>>> }
>>>> #endif
>>>>
>>>> +#if CONFIG_IS_ENABLED(BOOTSTAGE)
>>>> +ulong timer_get_boot_us(void)
>>>> +{
>>>> + u64 ticks = 0;
>>>> + u32 rate = 1;
>>>> + u64 us;
>>>> + int ret;
>>>> +
>>>> + ret = dm_timer_init();
>>>> + if (!ret) {
>>>> + /* The timer is available */
>>>> + rate = timer_get_rate(gd->timer);
>>>> + timer_get_count(gd->timer, &ticks);
>>>> + } else {
>>>> + return 0;
>>>> + }
>>>> +
>>>> + us = (ticks * 1000) / rate;
>>>> + return us;
>>>> +}
>>>> +#endif
>>>
>>> This is duplicate code in almost all the timer drivers, shouldn't
>>> this be a (weak) default implementation in timer-uclass.c?
>>
>> Yes. I was lazy and just copied this function and did not notice, that
>> even more timer drivers have this function. Of course it makes sense
>> to not duplicate code here, but have a common function for this. Frankly
>> I don't even know why exactly this function is needed, as I did not
>> look into BOOTSTAGE yet.
>>
>> Simon, do we really need this function? Can't bootstage just use the
>> "normal" timer functionality instead?
>
> It is needed because bootstage is called before driver model is ready.
> In fact it can be used to time driver model things.

I see, makes sense. This brings up my next questions though, why isn't
CONFIG_TIMER_EARLY enough in this case? AFAICT it's targeted exactly
for this early (pre DM) bootstage. From drivers/timer/Kconfig:

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
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
execution before driver model is set up. Enable this option to
use an early timer. These functions must be supported by your timer
driver: timer_early_get_count() and timer_early_get_rate().

So again, do we really need timer_get_boot_us() or isn't it enough
to select TIMER_EARLY when BOOTSTAGE is enabled?

Thanks,
Stefan

> The function here isn't that useful, since we cannot call
> dm_timer_init() before driver model is set up.
>
> The timer_get_boot_us() function can by in a timer driver, but must
> exist outside the driver infrastructure. It must init the hard and
> then return the correct time. One driver model probes the timer
> driver, it must then continue on in that way.
>
> Actually it looks like all the timers do this wrong. See
> arch/arm/mach-imx/syscounter.c or arch/arm/cpu/armv8/generic_timer.c
> for some ideas.

Thanks,
Stefan