drm/i915/fbc: Extract intel_fbc_max_cfb_height()

Pull the code to determine the maximum CFB height
into a separate function.

To make this work we need to declare an explicit max height
for all older platforms as well. But that is actually just
the max plane height as pre-HSW hardware supposedly doesn't
have the trick of leaving the extra lines uncompressed.
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240705145254.3355-12-ville.syrjala@linux.intel.comReviewed-by: Uma Shankar <uma.shankar@intel.com>

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

@@ -200,17 +200,30 @@ static unsigned int intel_fbc_cfb_stride(const struct intel_plane_state *plane_s
 	return _intel_fbc_cfb_stride(display, width, stride);
 }
 
-static unsigned int intel_fbc_cfb_size(const struct intel_plane_state *plane_state)
+/*
+ * Maximum height the hardware will compress, on HSW+
+ * additional lines (up to the actual plane height) will
+ * remain uncompressed.
+ */
+static unsigned int intel_fbc_max_cfb_height(struct intel_display *display)
 {
-	struct intel_display *display = to_intel_display(plane_state->uapi.plane->dev);
-	int height = drm_rect_height(&plane_state->uapi.src) >> 16;
+	struct drm_i915_private *i915 = to_i915(display->drm);
 
 	if (DISPLAY_VER(display) >= 8)
-		height = min(height, 2560);
-	else if (DISPLAY_VER(display) == 7)
-		height = min(height, 2048);
+		return 2560;
+	else if (DISPLAY_VER(display) >= 5 || IS_G4X(i915))
+		return 2048;
+	else
+		return 1536;
+}
+
+static unsigned int intel_fbc_cfb_size(const struct intel_plane_state *plane_state)
+{
+	struct intel_display *display = to_intel_display(plane_state->uapi.plane->dev);
+	unsigned int height = drm_rect_height(&plane_state->uapi.src) >> 16;
 
-	return height * intel_fbc_cfb_stride(plane_state);
+	return min(height, intel_fbc_max_cfb_height(display)) *
+		intel_fbc_cfb_stride(plane_state);
 }
 
 static u16 intel_fbc_override_cfb_stride(const struct intel_plane_state *plane_state)