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SubjectRe: [PATCH 18/37] dvb: let other frontends support FE_DISHNETWORK_SEND_LEGACY_CMD
Michael Krufky <mkrufky@m1k.net> wrote:
>
> +s32 timeval_usec_diff(struct timeval lasttime, struct timeval curtime)
> +{
> + return ((curtime.tv_usec < lasttime.tv_usec) ?
> + 1000000 - lasttime.tv_usec + curtime.tv_usec :
> + curtime.tv_usec - lasttime.tv_usec);
> +}
> +EXPORT_SYMBOL(timeval_usec_diff);
> +
> +static inline void timeval_usec_add(struct timeval *curtime, u32 add_usec)
> +{
> + curtime->tv_usec += add_usec;
> + if (curtime->tv_usec >= 1000000) {
> + curtime->tv_usec -= 1000000;
> + curtime->tv_sec++;
> + }
> +}

timeval arithmetic like this really shouldn't be hidden in a dvb driver -
it's generic code.

> +/*
> + * Sleep until gettimeofday() > waketime + add_usec
> + * This needs to be as precise as possible, but as the delay is
> + * usually between 2ms and 32ms, it is done using a scheduled msleep
> + * followed by usleep (normally a busy-wait loop) for the remainder
> + */
> +void dvb_frontend_sleep_until(struct timeval *waketime, u32 add_usec)
> +{
> + struct timeval lasttime;
> + s32 delta, newdelta;
> +
> + timeval_usec_add(waketime, add_usec);
> +
> + do_gettimeofday(&lasttime);
> + delta = timeval_usec_diff(lasttime, *waketime);
> + if (delta > 2500) {
> + msleep((delta - 1500) / 1000);
> + do_gettimeofday(&lasttime);
> + newdelta = timeval_usec_diff(lasttime, *waketime);
> + delta = (newdelta > delta) ? 0 : newdelta;
> + }
> + if (delta > 0)
> + udelay(delta);
> +}
> +EXPORT_SYMBOL(dvb_frontend_sleep_until);

However I don't believe that the driver should be using timevals and
do_gettimeofday() at all. Why not use jiffies-based timing like so
many other parts of the kernel?
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