On Thu, Dec 15, 2016 at 11:52:34AM +0200, Jani Nikula wrote: > On Thu, 15 Dec 2016, Nicholas Mc Guire <der.herr@xxxxxxx> wrote: > > On Thu, Dec 15, 2016 at 11:08:49AM +0200, Jani Nikula wrote: > >> On Thu, 15 Dec 2016, Nicholas Mc Guire <hofrat@xxxxxxxxx> wrote: > >> > Even on fast systems a 2 microsecond delay is most likely more efficient > >> > as a busy-wait loop. The overhead of a hrtimer does not seem warranted - > >> > change this to a udelay(2). > >> > >> Similar concerns as in [1]. We don't need the accuracy of udelay() here, > >> so this boils down to which is the better use of CPU. We could probably > >> relax the max delay more if that was helpful. But I'm not immediately > >> sold on "is most likely more efficient" which sounds like a gut feeling. > >> > >> I'm sorry it's not clear in my other reply that I do appreciate > >> addressing incorrect/silly use of usleep_range(); I'm just not (yet) > >> convinced udelay() is the answer. > > > > if the delay is not critical and all that is needed > > is an assurance that it is greater than X us then > > usleep_range is fine with a relaxed limit. > > So from what you wrote my patch proposal is wrong - the > > udelay() is not the way to got. > > My intent is to get rid of very small usleep_range() cases > > so if usleep_range(20,50) causes no issues with this driver > > and does not induce any performance penalty then that would > > be the way to go I think. > > Okay, so I looked at the code, and I looked at our spec, and I looked at > the MIPI D-PHY spec, and I cried a little. > > Long story short, I think usleep_range(10, 50) will be fine. Note that I really want to see a comment next to every delay like this documenting the actual hardware requirement, if the delay used by the code doesn't 100% match it. -- Ville Syrjälä Intel OTC _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/dri-devel
