自定义修改RK系列嵌入式板子uboot命令行界面分辨率

kernel/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c 作如下修改：
static int dw_hdmi_connector_get_modes(struct drm_connector *connector)
{
	struct dw_hdmi *hdmi = container_of(connector, struct dw_hdmi,
					     connector);
	struct edid *edid;
	struct drm_display_mode *mode;
	//const u8 def_modes[6] = {4, 16, 31, 19, 17, 2};
    //此处修改为自己要固定的分辨率vic。分辨率的结构体数组定义为在kernel/drivers/gpu/drm/drm_edid.c中定义的edid_cea_modes[]数组。
	const u8 def_modes[1] = {1};
	struct drm_display_info *info = &connector->display_info;
	struct hdr_static_metadata *metedata =
			&connector->display_info.hdmi.hdr_panel_metadata;
	int i, ret = 0;

	if (!hdmi->ddc)
		return 0;

	edid = drm_get_edid(connector, hdmi->ddc);
	//if (edid) {
    //直接将该处的edid注释，改成if(0)。执行else中的固定分辨率程序。
	if(0){
		dev_dbg(hdmi->dev, "got edid: width[%d] x height[%d]\n",
			edid->width_cm, edid->height_cm);

		hdmi->sink_is_hdmi = drm_detect_hdmi_monitor(edid);
		hdmi->sink_has_audio = drm_detect_monitor_audio(edid);
		drm_mode_connector_update_edid_property(connector, edid);
		cec_notifier_set_phys_addr_from_edid(hdmi->cec_notifier, edid);
		ret = drm_add_edid_modes(connector, edid);
		/* Store the ELD */
		drm_edid_to_eld(connector, edid);
		drm_mode_connector_update_hdr_property(connector, metedata);
		kfree(edid);
	} else {
		hdmi->sink_is_hdmi = true;
		hdmi->sink_has_audio = true;
		for (i = 0; i < sizeof(def_modes); i++) {
			mode = drm_display_mode_from_vic_index(connector,
							       def_modes,
							       31, i);
			if (mode) {
				if (!i)
					mode->type = DRM_MODE_TYPE_PREFERRED;
				drm_mode_probed_add(connector, mode);
				ret++;
			}
		}
		info->edid_hdmi_dc_modes = 0;
		info->hdmi.y420_dc_modes = 0;
		info->color_formats = 0;

		dev_info(hdmi->dev, "failed to get edid\n");
	}

	return ret;
}

kernel/drivers/gpu/drm/drm_edid.c 文件定义如下：
/*
 * Probably taken from CEA-861 spec.
 * This table is converted from xorg's hw/xfree86/modes/xf86EdidModes.c.
 *
 * Index using the VIC.
 */
static const struct drm_display_mode edid_cea_modes[] = {
	/* 0 - dummy, VICs start at 1 */
	{ },
	/* 1 - 640x480@60Hz */
	{ DRM_MODE("640x480", DRM_MODE_TYPE_DRIVER, 25175, 640, 656,
		   752, 800, 0, 480, 490, 492, 525, 0,
		   DRM_MODE_FLAG_NHSYNC | DRM_MODE_FLAG_NVSYNC),
	  .vrefresh = 60, .picture_aspect_ratio = HDMI_PICTURE_ASPECT_4_3, },
	/* 2 - 720x480@60Hz */
	{ DRM_MODE("720x480", DRM_MODE_TYPE_DRIVER, 27000, 720, 736,
		   798, 858, 0, 480, 489, 495, 525, 0,
		   DRM_MODE_FLAG_NHSYNC | DRM_MODE_FLAG_NVSYNC),
	  .vrefresh = 60, .picture_aspect_ratio = HDMI_PICTURE_ASPECT_4_3, },

即可改为640X480分辨率