Ping Do we have any consensus on the best way of handling this situation in the driver? On Mon, 2015-11-23 at 14:20 +0000, Deucher, Alexander wrote: > > -----Original Message----- > > From: Lyude [mailto:cpaul@xxxxxxxxxx] > > Sent: Sunday, November 22, 2015 9:45 PM > > To: Koenig, Christian; Daniel Stone > > Cc: Deucher, Alexander; David Airlie; dri-devel; Linux Kernel Mailing List; > > Jerome Glisse; Benjamin Tissoires > > Subject: Re: [PATCH] drm/radeon: Retry DDC probing on DVI on failure if we > > got an HPD interrupt > > > > On Sat, 2015-11-21 at 16:22 +0100, Christian König wrote: > > > On 21.11.2015 15:49, Daniel Stone wrote: > > > > Hi, > > > > > > > > On 21 November 2015 at 14:22, Christian König <christian.koenig@amd > > > > .com> wrote: > > > > > On 20.11.2015 16:52, cpaul@xxxxxxxxxx wrote: > > > > > > This is somewhat rare on most cards (depending on what angle > > > > > > you plug > > > > > > the DVI connector in), but on some cards it happens constantly. > > > > > > The > > > > > > Radeon R5 on the machine used for testing this patch for > > > > > > instance, runs > > > > > > into this issue just about every time I try to hotplug a DVI > > > > > > monitor and > > > > > > as a result hotplugging almost never works. > > > > > > > > > > > > Rescheduling the hotplug work for a second when we run into an > > > > > > HPD > > > > > > signal with a failing DDC probe usually gives enough time for > > > > > > the rest > > > > > > of the connector's pins to make contact, and fixes this issue. > > > > > > > > > > > > Signed-off-by: Stephen Chandler Paul <cpaul@xxxxxxxxxx> > > > > > > > > > > Yeah, that's something I always wondered a about bit as well. > > > > > > > > > > Debouncing is something very common done in electronics, but as > > > > > far as I > > > > > know the HPD pins don't necessary have an RC circuit so we might > > > > > need to > > > > > handle this case in software here. > > > > > > > > > > A delay of something between 10-30ms between the last HPD > > > > > interrupt and > > > > > further processing of the signal doesn't sounds like such a bad > > > > > idea. > > Unfortunately the delay needed to make hotplugging work on the system > > mentioned in the commit log can actually be over 700ms. > > > > > > > > > > Retrying on the other hand doesn't necessarily improve the > > > > > situation cause > > > > > the delay introduced by this might not be enough. > > Yeah, but I would think it would make sense to retry here so long as we > > back off after a certain time. This would also have the benefit of > > skipping this delay on systems that don't need it. > > > > > > > > > > So I would rather vote for a fixed delay between an HPD interrupt > > > > > and > > > > > actually starting to process anything. > > > > Yes-ish. Debouncing is useful, and ignoring buggy devices (e.g. > > > > those > > > > on marginal power) which send you HPD storms as well. But DP relies > > > > on > > > > 'short HPD' pulses which can be as brief as 2ms. So attempting to > > > > totally debounce all HPD won't work. > > > Well the discussion so far was about HPD on DVI only. > > > > > > I'm not so deep into DP, but why should it uses HPD pulses of less > > > than 2ms? > > This is part of the DP spec iirc. This being said though, the issue > > here with the HPD signal coming before the connector is ready only > > happens on DVI. I haven't ever run into this issue with any HDMI cables > > or DP cables, so I'm against imposing this on all connectors. > > > > One of the solutions I've been thinking about with this: In > > radeon_dvi_detect(), if we get a real hotplug signal retry the DDC > > probe until at least a second has passed, after which we back off and > > assume the port is disconnected. > > FWIW, there are registers to adjust how long the hpd needs to be asserted > before the hpd connection and short pulse interrupts are triggered. See > DC_HPDx_CONTROL. Maybe adjusting them would help. We currently just write > the default value, but it might be better to RMW the value in case there is a > special golden value set by the vbios at init time. > > Alex > > > > > > > Regards, > > > Christian. > > > > > > > > > > > Cheers, > > > > Daniel > > > > > -- > > Cheers, > > Lyude > -- Cheers, Lyude _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx http://lists.freedesktop.org/mailman/listinfo/dri-devel
