[SeaBIOS] [PATCH] Increase precision of usec timer calculation

[Stefan Berger]

On 11/01/2017 10:40 AM, Stefan Berger wrote:
> When timer_calc_usec() is used with large timeout falues, such as 60s,

obviously a typo ->values.

The problem occurred with the TPM driver where we are given usec values 
by the hardware and specs and want to call the timer_calc_usec() 
function. That function works well for small values but fails once the 
values become larger.

     Stefan

> the function lacks precision and produces different results than when
> using timer_calc(time / 1000) for the same timeout. This patch fixes
> the precision issue by falling back to timer_calc(time / 1000) for
> usec values over one second.
>
> Signed-off-by: Stefan Berger <stefanb at linux.vnet.ibm.com>
> ---
>   src/hw/timer.c | 2 ++
>   1 file changed, 2 insertions(+)
>
> diff --git a/src/hw/timer.c b/src/hw/timer.c
> index 03d22b2..2f0c864 100644
> --- a/src/hw/timer.c
> +++ b/src/hw/timer.c
> @@ -213,6 +213,8 @@ timer_calc(u32 msecs)
>   u32
>   timer_calc_usec(u32 usecs)
>   {
> +    if (usecs > 1000000)
> +        return timer_calc(usecs / 1000);
>       return timer_read() + DIV_ROUND_UP(GET_GLOBAL(TimerKHz) * usecs, 1000);
>   }
>