[PATCH] drm/i915/display: use old bpp as a base when modeset is not allowed

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We are currently observing failure on refresh rate change on VRR setup if
full modeset is not allowed. This is caused by the mismatch in bpp
configured by GOP and bpp value calculated by our driver. Changing bpp to
value calculated by our driver would require full mode set.

We don't have mechanism to communicate current bpp to userspace ->
Userspace can't request to use current bpp. Changing bpp means full
modeset. This becomes a problem when userspace haven't allowed full mode
set.

Complete solution here would mean adding mechanism to communicate current
bpp to userspace. User space should use this bpp to avoid changing bpp if
it wants to avoid full mode set.

Tackle this for now in our driver by using existing bpp if full modeset is
not allowed.

Signed-off-by: Jouni Högander <jouni.hogander@xxxxxxxxx>
---
 drivers/gpu/drm/i915/display/intel_display.c | 33 ++++++++++++++------
 1 file changed, 23 insertions(+), 10 deletions(-)

diff --git a/drivers/gpu/drm/i915/display/intel_display.c b/drivers/gpu/drm/i915/display/intel_display.c
index 9049b9a1209d8..7b805998b280a 100644
--- a/drivers/gpu/drm/i915/display/intel_display.c
+++ b/drivers/gpu/drm/i915/display/intel_display.c
@@ -4385,21 +4385,34 @@ compute_baseline_pipe_bpp(struct intel_atomic_state *state,
 			  struct intel_crtc *crtc)
 {
 	struct drm_i915_private *dev_priv = to_i915(crtc->base.dev);
-	struct intel_crtc_state *crtc_state =
+	struct intel_crtc_state *new_crtc_state =
 		intel_atomic_get_new_crtc_state(state, crtc);
+	struct intel_crtc_state *old_crtc_state =
+		intel_atomic_get_old_crtc_state(state, crtc);
 	struct drm_connector *connector;
 	struct drm_connector_state *connector_state;
 	int bpp, i;
 
-	if ((IS_G4X(dev_priv) || IS_VALLEYVIEW(dev_priv) ||
-	    IS_CHERRYVIEW(dev_priv)))
-		bpp = 10*3;
-	else if (DISPLAY_VER(dev_priv) >= 5)
-		bpp = 12*3;
-	else
-		bpp = 8*3;
+	/*
+	 * TODO: We don't have mechanism to communicate current bpp to
+	 * userspace -> Userspace can't request to use current bpp. Changing bpp
+	 * means full modeset. This becomes a problem when userspace wants to
+	 * avoid full modeset. Tackle this on our driver by using existing bpp
+	 * if full modeset is not allowed.
+	 */
+	if (!state->base.allow_modeset) {
+		bpp = old_crtc_state->pipe_bpp;
+	} else {
+		if ((IS_G4X(dev_priv) || IS_VALLEYVIEW(dev_priv) ||
+		     IS_CHERRYVIEW(dev_priv)))
+			bpp = 10 * 3;
+		else if (DISPLAY_VER(dev_priv) >= 5)
+			bpp = 12 * 3;
+		else
+			bpp = 8 * 3;
+	}
 
-	crtc_state->pipe_bpp = bpp;
+	new_crtc_state->pipe_bpp = bpp;
 
 	/* Clamp display bpp to connector max bpp */
 	for_each_new_connector_in_state(&state->base, connector, connector_state, i) {
@@ -4408,7 +4421,7 @@ compute_baseline_pipe_bpp(struct intel_atomic_state *state,
 		if (connector_state->crtc != &crtc->base)
 			continue;
 
-		ret = compute_sink_pipe_bpp(connector_state, crtc_state);
+		ret = compute_sink_pipe_bpp(connector_state, new_crtc_state);
 		if (ret)
 			return ret;
 	}
-- 
2.34.1




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