On Tue, Jul 17, 2018 at 06:05:51PM -0700, Nathan Ciobanu wrote: > On Tue, Jul 17, 2018 at 03:21:17PM -0700, Dhinakaran Pandiyan wrote: > > On Mon, 2018-07-16 at 16:51 -0700, Marc Herbert wrote: > > > > > > > > > > > > > > I think the bug is with this infinite loop which is at the mercy > > > > > of an external device > > > > > and in my case I have this MST hub which appears to be DP 1.2 > > > > > that triggers the > > > > > infinite loop case. We have to limit the number of iterations and > > > > > DP 1.4 spec happened to fix this issue. I'm a newbie in this area > > > > > but in this case > > > > > shouldn't we apply the same counter to all <= "DP 1.4" devices? > > > > ok, the infinite loop situation is really bad... but I don't > > > > believe > > > > we are going with the right fix... > > > > and a good indication is that your fix is for DP-1.4 while your bug > > > > is seeing on DP-1.2 > > > I thought the only reason the infinite loop fix isn't in 1.2 is just > > > because there's > > > no 1.2.1 spec... (plus the naive assumption that buggy sinks don't > > > exist) > > > > > Irrespective of whether the sink is DP1.2 or 1.4, if there are sinks > > out there that keep toggling between two values there should be an > > overall limit to how many times this loop gets executed. Even if this > > isn't right fix for the issue at hand, the loop has to break. > > > > Then there's the question of what the limit should be. We could use the > > DP1.4 limit as a reference and apply it widely. But there's a problem > > here, we have 4 vswing values and 4 pre-emphasis values. If the sink > > progressively changes one variable at a time, we'll need at least 16 > > iterations. Nathan's patch here will prematurely error out and that > > doesn't sound reasonable to impose on non DP1.4 sinks. > > I think it would be a max of 13 iterations since one of the vswing > values will be max_vswing and the loop will terminate at that point > without trying the other 3 preemph values for that voltage, correct?
I was talking to DK yesterday and he suggested that we should go with a huge number for DP_1.2 and with the spec for DP_1.4. According to DK 80 was covering all combinations few times. So you get your patch and create some max_cr_tries = dp_1.4 ? spec : 80; or something like that. I think I like that because infinite loop situation here is so bad and we should avoid even if it was something else that got really wrong. Thanks, Rodrigo. > > -Nathan > > > > -DK > > > > > > > > > > > > > _______________________________________________ > > > Intel-gfx mailing list > > > Intel-gfx@lists.freedesktop.org > > > https://lists.freedesktop.org/mailman/listinfo/intel-gfx > > > _______________________________________________ > Intel-gfx mailing list > Intel-gfx@lists.freedesktop.org > https://lists.freedesktop.org/mailman/listinfo/intel-gfx _______________________________________________ Intel-gfx mailing list Intel-gfx@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/intel-gfx
