drm/i915: Fix MSO vs. bigjoiner timings confusion

When calculating pipe_mode and when doing readout we need
to order our steps correctly.

1. We start with adjusted_mode crtc timings being populated
   with the transcoder timings (either via readout or
   compute_config(). These will be per-segment for MSO.
2. For all other uses we want the full crtc timings so
   we ask intel_splitter_adjust_timings() to expand
   the per-segment numbers to their full glory
3. If bigjoiner is used we the divide the full numbers
   down to per-pipe numbers using intel_bigjoiner_adjust_timings()

During readout we also have to reconstruct the adjusted_mode
normal timings (ie. not the crtc_ stuff). These are supposed
to reflect the full timings of the display. So we grab these
between steps 2 and 3.

The "user" mode readout (mainly done for fastboot purposes)
should be whatever mode the user would have used had they
asked us to do a modeset. We want the full timings for this
as the per-segment timings are not suppoesed to be user visible.
Also the user mode normal timings hdisplay/vdisplay need to
match PIPESRC (that is where we get our PIPESRC size
we doing a modeset with a user supplied mode).

And we end up with
- adjusted_mode normal timigns == full timings
- adjusted_mode crtc timings == transcoder timings
  (per-segment timings for MSO, full timings otherwise)
- pipe_mode normal/crtc timings == pipe timings
  (full timings divided by the number of bigjoiner pipes, if any)
- user mode normal timings == full timings with
  hdisplay/vdisplay replaced with PIPESRC size
- user mode crtc timings == full timings

Yes, that is a lot of timings. One day we'll try to remove
some of the ones we don't actually need to keep around...
Reviewed-by: Manasi Navare <manasi.d.navare@intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220223131315.18016-10-ville.syrjala@linux.intel.com

drivers/gpu/drm/i915/display/intel_display.c

@@ -2773,25 +2773,33 @@ static void intel_crtc_readout_derived_state(struct intel_crtc_state *crtc_state
 	struct drm_display_mode *pipe_mode = &crtc_state->hw.pipe_mode;
 	struct drm_display_mode *adjusted_mode = &crtc_state->hw.adjusted_mode;
 
+	/*
+	 * Start with the adjusted_mode crtc timings, which
+	 * have been filled with the transcoder timings.
+	 */
 	drm_mode_copy(pipe_mode, adjusted_mode);
 
-	intel_bigjoiner_adjust_timings(crtc_state, pipe_mode);
-
-	if (crtc_state->splitter.enable) {
+	/* Expand MSO per-segment transcoder timings to full */
 	intel_splitter_adjust_timings(crtc_state, pipe_mode);
 
-		intel_mode_from_crtc_timings(pipe_mode, pipe_mode);
+	/*
+	 * We want the full numbers in adjusted_mode normal timings,
+	 * adjusted_mode crtc timings are left with the raw transcoder
+	 * timings.
+	 */
 	intel_mode_from_crtc_timings(adjusted_mode, pipe_mode);
-	} else {
-		intel_mode_from_crtc_timings(pipe_mode, pipe_mode);
-		intel_mode_from_crtc_timings(adjusted_mode, adjusted_mode);
-	}
-
-	intel_crtc_compute_pixel_rate(crtc_state);
 
-	drm_mode_copy(mode, adjusted_mode);
+	/* Populate the "user" mode with full numbers */
+	drm_mode_copy(mode, pipe_mode);
+	intel_mode_from_crtc_timings(mode, mode);
 	mode->hdisplay = crtc_state->pipe_src_w << crtc_state->bigjoiner;
 	mode->vdisplay = crtc_state->pipe_src_h;
+
+	/* Derive per-pipe timings in case bigjoiner is used */
+	intel_bigjoiner_adjust_timings(crtc_state, pipe_mode);
+	intel_mode_from_crtc_timings(pipe_mode, pipe_mode);
+
+	intel_crtc_compute_pixel_rate(crtc_state);
 }
 
 static void intel_encoder_get_config(struct intel_encoder *encoder,
@@ -2840,15 +2848,21 @@ static int intel_crtc_compute_pipe_mode(struct intel_crtc_state *crtc_state)
 {
 	struct intel_crtc *crtc = to_intel_crtc(crtc_state->uapi.crtc);
 	struct drm_i915_private *i915 = to_i915(crtc->base.dev);
+	struct drm_display_mode *adjusted_mode = &crtc_state->hw.adjusted_mode;
 	struct drm_display_mode *pipe_mode = &crtc_state->hw.pipe_mode;
 	int clock_limit = i915->max_dotclk_freq;
 
-	drm_mode_copy(pipe_mode, &crtc_state->hw.adjusted_mode);
-
-	intel_bigjoiner_adjust_timings(crtc_state, pipe_mode);
+	/*
+	 * Start with the adjusted_mode crtc timings, which
+	 * have been filled with the transcoder timings.
+	 */
+	drm_mode_copy(pipe_mode, adjusted_mode);
 
+	/* Expand MSO per-segment transcoder timings to full */
 	intel_splitter_adjust_timings(crtc_state, pipe_mode);
 
+	/* Derive per-pipe timings in case bigjoiner is used */
+	intel_bigjoiner_adjust_timings(crtc_state, pipe_mode);
 	intel_mode_from_crtc_timings(pipe_mode, pipe_mode);
 
 	if (DISPLAY_VER(i915) < 4) {