[Bug 103347] [dp] intel_dp.c:1554 WARN_ON(len <=8)

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=103347

--- Comment #34 from Ville Syrjala <ville.syrjala at linux.intel.com> ---
(In reply to F.Hartung from comment #33)
> (In reply to Ville Syrjala from comment #32)
> > This looks to be a more or less the same issue as bug 106291.
> > 
> > If I understood correctly this connector/edid overriding is a basically
> > workaround for Kodi failing to do anything sensible when there are no
> > displays connected. I'd say the correct thing to do is to fix this in Kodi.
> > 
> > I've rambled on a bit in the other bug on how we might make connector
> > forcing work a bit better for LSPCON/DP branch devices. But for straight up
> > DP ports with nothing truly connected I don't think we can make this do
> > anything sane, ever (unless we implement a simulated DP sink in the kernel
> > to take the role of the real thing).
> 
> Indeed this looks like a related problem. I'm just confused why the forced
> edid worked with kernel 4.14.x, worked with kernel 4.15.x with the error
> messages and finally is broken in 4.16.8. I get the error messages but no
> output at all.
> Since I use the same LibreELEC base and just switch the kernel version it
> looks like it's related to some driver changes.

I guess we're now pruning out all the modes, and before we didn't for some
reason.

A hack like this might help a bit. Though it will still prune the modes quite
severly.

diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
index 62f82c4298ac..0f2ad4983582 100644
--- a/drivers/gpu/drm/i915/intel_dp.c
+++ b/drivers/gpu/drm/i915/intel_dp.c
@@ -6292,8 +6292,14 @@ intel_dp_init_connector(struct intel_digital_port
*intel_dig_port,
                return false;

        intel_dp_set_source_rates(intel_dp);
+       intel_dp->dpcd[DP_MAX_LINK_RATE] = DP_LINK_BW_1_62;
+       intel_dp_set_sink_rates(intel_dp);
+       intel_dp_set_common_rates(intel_dp);

+       intel_dp->max_link_lane_count = 1;
+       intel_dp->max_link_rate = 162000;
        intel_dp->reset_link_params = true;
+
        intel_dp->pps_pipe = INVALID_PIPE;
        intel_dp->active_pipe = INVALID_PIPE;

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