The patch below does not apply to the 5.5-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.
thanks,
greg k-h
------------------ original commit in Linus's tree ------------------
From 2e0a576511f656933adfe56ef03b9cf3e64b21b7 Mon Sep 17 00:00:00 2001
From: Jani Nikula jani.nikula@intel.com Date: Thu, 13 Feb 2020 16:04:11 +0200 Subject: [PATCH] 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.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 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-stanisl... (cherry picked from commit a4277aa398d76db109d6b8420934f68daf69a6c3) Signed-off-by: Jani Nikula jani.nikula@intel.com
diff --git a/drivers/gpu/drm/i915/display/intel_display.c b/drivers/gpu/drm/i915/display/intel_display.c index 064dd99bbc49..e68ec25fc97c 100644 --- a/drivers/gpu/drm/i915/display/intel_display.c +++ b/drivers/gpu/drm/i915/display/intel_display.c @@ -17433,6 +17433,24 @@ 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"); + } } }