Re: [PATCH 0/6] Enable CONFIG_TIMER for all Kirwood / MVEBU boards

Stefan Herbrechtsmeier
2022-09-01T11:52:49Z

Hi,

Am 01.09.2022 um 11:27 schrieb Stefan Roese:
> Hi Tony,
>
> On 01.09.22 09:39, Tony Dinh wrote:
>
> <snip>
>
>>>> Some ideas.
>>>>
>>>> The get_timer() function looks wrong assigning an uint64_t to ulong.
>>>>
>>>> lib/time.c
>>>>
>>>>       static uint64_t notrace tick_to_time(uint64_t tick)
>>>>       uint64_t notrace get_ticks(void)
>>>>       uint64_t __weak notrace get_ticks(void)
>>>>
>>>>       ulong __weak get_timer(ulong base)
>>>>       {
>>>>               return tick_to_time(get_ticks()) - base;
>>>>       }
>>>>
>>>> Most of the timer infrastructure is using uint64_t. I'm seeing this
>>>> __weak function get_timer was invoked in Kirkwood boards. Both in
>>>> sleep and timer commands.
>>>
>>> The get_ticks() thing can run at 1MHz but the timer is 1KHz, so that
>>> is why we don't need a u64 for the timer.
>>
>> Thanks for your explanation! However, would you agree that code is
>> problematic and needed some improvement ? IOW, depending what the
>> compiler does, it might return the 1st 32 bit of the 64-bit integer
>> result?
>
> It will return the lower 32 bits if the system is 32bit, yes.
>
> To check if we have a problem here, please add this (totally untested)
> code and extend it if it makes sense:
>
> diff --git a/lib/time.c b/lib/time.c
> index bbf191f67323..ef5252419f3b 100644
> --- a/lib/time.c
> +++ b/lib/time.c
> @@ -146,7 +146,15 @@ int __weak timer_init(void)
>  /* Returns time in milliseconds */
>  ulong __weak get_timer(ulong base)
>  {
> -       return tick_to_time(get_ticks()) - base;
> +       u64 ticks = get_ticks();
> +       u64 time_ms = tick_to_time(ticks);
> +
> +       if (time_ms & 0xffffffff00000000ULL)
> +               printf("ticks=%lld time_ms=%lld\n", ticks, time_ms);
> +       if ((time_ms - base) & 0xffffffff80000000ULL)
> +               printf("ticks=%lld time_ms=%lld base=%ld ret=%lld\n",
> ticks, time_ms, base, time_ms - base);
> +
> +       return time_ms - base;
>  }
>
> At least here, you seem to have a wrap around with the 32bits AFAICT:
>
>> GoFlexHome> sleep 20.5
>> do_sleep got a timer start = 15031
>> do_sleep delay = 20000
>> do_sleep delay = 20500
>> do_sleep sleeping...
>> do_sleep start 15031 current 100
>> <snip>
>> do_sleep start 15031 current 6400
>> do_sleep end of sleep ... current = 4294952265
>>
>> *** Something strange happened here. current should be 6500, but it
>> seems to have garbage. So the loop exits prematurely.
>
> 4294952265 = 0xFFFFC549!
>

Does the driver use a 32 bit counter without the timer_conv_64 function
inside the get_count function?

Regards
Stefan