drm/i915/dsc: force full modeset whenever DSC is enabled at probe

We lack full state readout of DSC config, which may lead to DSC enable
using a config that's all zeros, failing spectacularly. Force full
modeset and thus compute config at probe to get a sane state, until we
implement DSC state readout. Any fastset that did appear to work with
DSC at probe, worked by coincidence. [1] is an example of a change that
triggered the issue on TGL DSI DSC.

[1] http://patchwork.freedesktop.org/patch/msgid/20200212150102.7600-1-ville.syrjala@linux.intel.com

Cc: Manasi Navare <manasi.d.navare@intel.com>
Cc: Vandita Kulkarni <vandita.kulkarni@intel.com>
Cc: Ville Syrjala <ville.syrjala@linux.intel.com>
Cc: stable@vger.kernel.org
Fixes: fbacb15ea814 ("drm/i915/dsc: add basic hardware state readout support")
Acked-by: Matt Roper <matthew.d.roper@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200213140412.32697-3-stanislav.lisovskiy@intel.com

diff --git a/drivers/gpu/drm/i915/display/intel_display.c b/drivers/gpu/drm/i915/display/intel_display.c
index 61ba1f2256a03586a73a06a8ef3a7553447617c1..1e3f2cc27db8e39a9ad36913a47607f95eff682f 100644 (file)
--- a/drivers/gpu/drm/i915/display/intel_display.c
+++ b/drivers/gpu/drm/i915/display/intel_display.c
@@ -17828,6 +17828,24 @@ retry:
                         * have readout for pipe gamma enable.
                         */
                        crtc_state->uapi.color_mgmt_changed = true;
+
+                       /*
+                        * FIXME hack to force full modeset when DSC is being
+                        * used.
+                        *
+                        * As long as we do not have full state readout and
+                        * config comparison of crtc_state->dsc, we have no way
+                        * to ensure reliable fastset. Remove once we have
+                        * readout for DSC.
+                        */
+                       if (crtc_state->dsc.compression_enable) {
+                               ret = drm_atomic_add_affected_connectors(state,
+                                                                        &crtc->base);
+                               if (ret)
+                                       goto out;
+                               crtc_state->uapi.mode_changed = true;
+                               drm_dbg_kms(dev, "Force full modeset for DSC\n");
+                       }
                }
        }