On Mon, Dec 14, 2015 at 04:48:09PM +0200, Ville Syrjälä wrote: > On Mon, Dec 14, 2015 at 02:21:56PM +0100, Thierry Reding wrote: > > From: Thierry Reding <treding@xxxxxxxxxx> > > > > Use microsecond sleeps for the clock recovery and channel equalization > > delays during link training. The duration of these delays can be from > > 100 us up to 16 ms. It is rude to busy-loop for that amount of time. > > Do you have some numbers on how this affects a typical link training > cycle? Not really. Sinks aren't required to provide a value here, in which case the specification says that a default of 100 us and 400 us should be used for clock recovery and channel equalization, respectively. If the sink provides an AUX_RD_INTERVAL value, it is used for both CR and CE (and is in units of 4 ms). Best case a typical link training cycle would therefore take something like 0.5 ms and worst case, since the number of retries should be limited to 5, it'd be around 5 * 16 ms = 80 ms. That's not counting the actual AUX transactions, though they should be pretty fast. Since this patch uses usleep_range(min, min * 2) the worst case now becomes ~ 160 ms. That's still not very much from a responsiveness point of view, but the upside is of course that there are no busy loops that could potentially hog the CPU. Thierry
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