On Mon, Feb 01, 2016 at 07:27:53PM +0530, Durgadoss R wrote: > To support USB type C alternate DP mode, the display driver needs to > know the number of lanes required by the DP panel as well as number > of lanes that can be supported by the type-C cable. Sometimes, the > type-C cable may limit the bandwidth even if Panel can support > more lanes. To address these scenarios, the display driver will > start link training with max lanes, and if that fails, the driver > falls back to x2 lanes; and repeats this procedure for all > bandwidth/lane configurations. > > * Since link training is done before modeset only the port > (and not pipe/planes) and its associated PLLs are enabled. > * On DP hotplug: Directly start link training on the crtc > associated with the DP encoder. > * On Connected boot scenarios: When booted with an LFP and a DP, > typically, BIOS brings up DP. In these cases, we disable the > crtc, do upfront link training and then re-enable it back. > * All local changes made for upfront link training are reset > to their previous values once it is done; so that the > subsequent modeset is not aware of these changes. Glancing over this stuff, it doesn't look all that good on the locking front. Mainly there doesn't seem to locking. In general I'm not really convinced upfront link training is a very good idea if it needs a pipe. What happens if we fail to find a free pipe? I'd be much happier about this if we could make do without a pipe at least on some modern platforms and actually limit the feature to those platforms. PLLs are another concern, but I think modern platforms often have some kind of way to always get the standard DP frequencies from eg. the LCPLL. If we do go with the "hope you find a free pipe" approach, then it really needs to do that atomic locking stuff right. Otherwise I'd expect fireworks when someone plugs in a display while there's modeset happening. -- Ville Syrjälä Intel OTC _______________________________________________ Intel-gfx mailing list Intel-gfx@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/intel-gfx
