drm/i915/fbc: Split plane pixel format checks per-platform

Carve up pixel_format_is_valid() into per-platform variants to
make it easier to see what limits are actually being imposed.

Note that the XRGB1555 can be dropped from the g4x+ variant
since the plane no longer supports that format anyway.

TODO: maybe go for vfuncs later

v2: Update for lnl changes

Reviewed-by: Juha-Pekka Heikkila <juhapekka.heikkila@gmail.com> #v1
Reviewed-by: Vinod Govindapillai <vinod.govindapillai@intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20231003194256.28569-5-ville.syrjala@linux.intel.com

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

@@ -917,7 +917,7 @@ static bool stride_is_valid(const struct intel_plane_state *plane_state)
 		return i8xx_fbc_stride_is_valid(plane_state);
 }
 
-static bool pixel_format_is_valid(const struct intel_plane_state *plane_state)
+static bool i8xx_fbc_pixel_format_is_valid(const struct intel_plane_state *plane_state)
 {
 	struct drm_i915_private *i915 = to_i915(plane_state->uapi.plane->dev);
 	const struct drm_framebuffer *fb = plane_state->hw.fb;
@@ -931,20 +931,59 @@ static bool pixel_format_is_valid(const struct intel_plane_state *plane_state)
 		/* 16bpp not supported on gen2 */
 		if (DISPLAY_VER(i915) == 2)
 			return false;
+		return true;
+	default:
+		return false;
+	}
+}
+
+static bool g4x_fbc_pixel_format_is_valid(const struct intel_plane_state *plane_state)
+{
+	struct drm_i915_private *i915 = to_i915(plane_state->uapi.plane->dev);
+	const struct drm_framebuffer *fb = plane_state->hw.fb;
+
+	switch (fb->format->format) {
+	case DRM_FORMAT_XRGB8888:
+	case DRM_FORMAT_XBGR8888:
+		return true;
+	case DRM_FORMAT_RGB565:
 		/* WaFbcOnly1to1Ratio:ctg */
 		if (IS_G4X(i915))
 			return false;
 		return true;
+	default:
+		return false;
+	}
+}
+
+static bool lnl_fbc_pixel_format_is_valid(const struct intel_plane_state *plane_state)
+{
+	const struct drm_framebuffer *fb = plane_state->hw.fb;
+
+	switch (fb->format->format) {
+	case DRM_FORMAT_XRGB8888:
+	case DRM_FORMAT_XBGR8888:
 	case DRM_FORMAT_ARGB8888:
 	case DRM_FORMAT_ABGR8888:
-		if (DISPLAY_VER(i915) >= 20)
-			return true;
-		fallthrough;
+	case DRM_FORMAT_RGB565:
+		return true;
 	default:
 		return false;
 	}
 }
 
+static bool pixel_format_is_valid(const struct intel_plane_state *plane_state)
+{
+	struct drm_i915_private *i915 = to_i915(plane_state->uapi.plane->dev);
+
+	if (DISPLAY_VER(i915) >= 20)
+		return lnl_fbc_pixel_format_is_valid(plane_state);
+	else if (DISPLAY_VER(i915) >= 5 || IS_G4X(i915))
+		return g4x_fbc_pixel_format_is_valid(plane_state);
+	else
+		return i8xx_fbc_pixel_format_is_valid(plane_state);
+}
+
 static bool i8xx_fbc_rotation_is_valid(const struct intel_plane_state *plane_state)
 {
 	return plane_state->hw.rotation == DRM_MODE_ROTATE_0;