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.syr...

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 Signed-off-by: Jani Nikula jani.nikula@intel.com --- drivers/gpu/drm/i915/display/intel_display.c | 18 ++++++++++++++++++ 1 file changed, 18 insertions(+)

diff --git a/drivers/gpu/drm/i915/display/intel_display.c b/drivers/gpu/drm/i915/display/intel_display.c index e09d3c93c52b..c1c392e2e8c3 100644 --- a/drivers/gpu/drm/i915/display/intel_display.c +++ b/drivers/gpu/drm/i915/display/intel_display.c @@ -17835,6 +17835,24 @@ static int intel_initial_commit(struct drm_device *dev) * 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"); + } } }