On 25/08/2019 23:23, Ilia Mirkin wrote:
You'll probably get a more detailed reply during the week, but for now have a look at the "link-status" property, which was made for precisely this situation. I think basically the idea is to ignore link training as part of the modeset, and just return the link status depending on the success. (And you should filter out totally infeasible modes, i.e. outside the monitor's max lanes/bandwidth capabilities, which I believe are available via DPCD or EDID.) See https://www.kernel.org/doc/html/latest/gpu/drm-kms.html for a bit more info as well.
We've got similar issue with HDMI too. If HPD first goes low, then high, but the userspace hasn't handled the HPD event in between, the userspaces I looked at just think that nothing has happened.
So maybe any time there's a HPD -> low, we should set link-status to bad, hope that userspace knows about the property, and at next modeset, set it back to good.
Tomi
Cheers, -ilia On Sun, Aug 25, 2019 at 7:12 AM Jyri Sarha <jsarha@xxxxxx> wrote:Hi, I am working on a new DisplayPort bridge-driver and there is a couple of things that I do not know how to handle. 1. When should the link training happen? a) In connector detect()? - This would enable us to do mode filtering (in mode_valid()) based on the established link band-width (then again mode_valid() documentation suggests that modes should only be filtered based on "configuration-invariant hardware constraints"). b) In check phase (this would currently mean mode_fixup)? - This is the last point where we can reject a mode that can not be sent over the DP-link c) In commit phase (e.g. bridge enable()) - This is bad since we should not fail any more in the commit phase 2. DP-link sometimes drops after a succesful link training and DP-sink is supposed to send short HPD pulse about it. What are the recommended ways to handle the situation? a) Send hotplug event and let the DRM client deal with it? - This does not work too well because even if the client tries to restore the display by committing the same state again - like fbdev does - the bridge does not go trough disable-enable cycle, since display mode has not changed. - Despite it not working so well, this is what the most drivers appear to do. b) Driver internally re-trains the link but send a hotplug event always after it? - This is what i915 does, if I read the code right. - How to treat a training failure? Sending hotplug event does not really help (see above). c) Silently re-train the link if we were able to restore the link and the display mode, and send HPD only if something went wrong? Best regards, Jyri -- Texas Instruments Finland Oy, Porkkalankatu 22, 00180 Helsinki. Y-tunnus/Business ID: 0615521-4. Kotipaikka/Domicile: Helsinki _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/dri-devel
-- Texas Instruments Finland Oy, Porkkalankatu 22, 00180 Helsinki. Y-tunnus/Business ID: 0615521-4. Kotipaikka/Domicile: Helsinki _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/dri-devel
