[Bug 89661] [ivb] Unable to configure 3rd pipe (e.g. LVDS + DP + DP)

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=89661

--- Comment #25 from Ville Syrjala <ville.syrjala at linux.intel.com> ---
The problem is that we may end up using 1.62 link rate for one DP port, and 2.7
for the other DP port, leaving no free DPLLs for the non-DP port.

Fixing this requires that we'd consider the failure to find a DPLL as a reason
to retry in the bw_constrained mode (or some similar mode) and made the DP link
rate selection try to pick a common rate for all ports.

I have a branch [1] that cleans up some of the retry logic to better deal with
FDI bifurcation (another common reason for failed 3 pipe configuration on IVB),
but it doesn't deal with this DPLL issue. IIRC one problem is that we do the
DPLL computation way too late to retry easily. I think we'd have to move it a
bit, which would also allow us to use the accurate clock in various check
functions. And then we'd need to adjust the DP compute_config logic to pick a
common rate somehow (just go for the max?). Anyways, I think my bifurcation
branch might be a decent first step in making the retry logic nicer.

[1] git://github.com/vsyrjala/linux.git ivb_bifurcation_atomic_7

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