-/**
- * intel_choose_pipe_bpp_dither - figure out what color depth the pipe should send
- * @crtc: CRTC structure
- * @mode: requested mode
- *
- * A pipe may be connected to one or more outputs. Based on the depth of the
- * attached framebuffer, choose a good color depth to use on the pipe.
- *
- * If possible, match the pipe depth to the fb depth. In some cases, this
- * isn't ideal, because the connected output supports a lesser or restricted
- * set of depths. Resolve that here:
- * LVDS typically supports only 6bpc, so clamp down in that case
- * HDMI supports only 8bpc or 12bpc, so clamp to 8bpc with dither for 10bpc
- * Displays may support a restricted set as well, check EDID and clamp as
- * appropriate.
- * DP may want to dither down to 6bpc to fit larger modes
- *
- * RETURNS:
- * Dithering requirement (i.e. false if display bpc and pipe bpc match,
- * true if they don't match).
- */
-static bool intel_choose_pipe_bpp_dither(struct drm_crtc *crtc,
- struct drm_framebuffer *fb,
- unsigned int *pipe_bpp,
- struct drm_display_mode *mode)
-{
- struct drm_device *dev = crtc->dev;
- struct drm_i915_private *dev_priv = dev->dev_private;
- struct drm_connector *connector;
- struct intel_encoder *intel_encoder;
- unsigned int display_bpc = UINT_MAX, bpc;
-
- /* Walk the encoders & connectors on this crtc, get min bpc */
- for_each_encoder_on_crtc(dev, crtc, intel_encoder) {
-
- if (intel_encoder->type == INTEL_OUTPUT_LVDS) {
- unsigned int lvds_bpc;
-
- if ((I915_READ(PCH_LVDS) & LVDS_A3_POWER_MASK) ==
- LVDS_A3_POWER_UP)
- lvds_bpc = 8;
- else
- lvds_bpc = 6;
-
- if (lvds_bpc < display_bpc) {
- DRM_DEBUG_KMS("clamping display bpc (was %d) to LVDS (%d)\n", display_bpc, lvds_bpc);
- display_bpc = lvds_bpc;
- }
- continue;
- }
-
- /* Not one of the known troublemakers, check the EDID */
- list_for_each_entry(connector, &dev->mode_config.connector_list,
- head) {
- if (connector->encoder != &intel_encoder->base)
- continue;
-
- /* Don't use an invalid EDID bpc value */
- if (connector->display_info.bpc &&
- connector->display_info.bpc < display_bpc) {
- DRM_DEBUG_KMS("clamping display bpc (was %d) to EDID reported max of %d\n", display_bpc, connector->display_info.bpc);
- display_bpc = connector->display_info.bpc;
- }
- }
-
- if (intel_encoder->type == INTEL_OUTPUT_EDP) {
- /* Use VBT settings if we have an eDP panel */
- unsigned int edp_bpc = dev_priv->edp.bpp / 3;
-
- if (edp_bpc && edp_bpc < display_bpc) {
- DRM_DEBUG_KMS("clamping display bpc (was %d) to eDP (%d)\n", display_bpc, edp_bpc);
- display_bpc = edp_bpc;
- }
- continue;
- }
-
- /*
- * HDMI is either 12 or 8, so if the display lets 10bpc sneak
- * through, clamp it down. (Note: >12bpc will be caught below.)
- */
- if (intel_encoder->type == INTEL_OUTPUT_HDMI) {
- if (display_bpc > 8 && display_bpc < 12) {
- DRM_DEBUG_KMS("forcing bpc to 12 for HDMI\n");
- display_bpc = 12;
- } else {
- DRM_DEBUG_KMS("forcing bpc to 8 for HDMI\n");
- display_bpc = 8;
- }
- }
- }
-
- if (mode->private_flags & INTEL_MODE_DP_FORCE_6BPC) {
- DRM_DEBUG_KMS("Dithering DP to 6bpc\n");
- display_bpc = 6;
- }
-
- /*
- * We could just drive the pipe at the highest bpc all the time and
- * enable dithering as needed, but that costs bandwidth. So choose
- * the minimum value that expresses the full color range of the fb but
- * also stays within the max display bpc discovered above.
- */
-
- switch (fb->depth) {
- case 8:
- bpc = 8; /* since we go through a colormap */
- break;
- case 15:
- case 16:
- bpc = 6; /* min is 18bpp */
- break;
- case 24:
- bpc = 8;
- break;
- case 30:
- bpc = 10;
- break;
- case 48:
- bpc = 12;
- break;
- default:
- DRM_DEBUG("unsupported depth, assuming 24 bits\n");
- bpc = min((unsigned int)8, display_bpc);
- break;
- }
-
- display_bpc = min(display_bpc, bpc);
-
- DRM_DEBUG_KMS("setting pipe bpc to %d (max display bpc %d)\n",
- bpc, display_bpc);
-
- *pipe_bpp = display_bpc * 3;
-
- return display_bpc != bpc;
-}
-