OK3568 4.19.206 Buildroot Fixed HDMI Resolution

Document classification: □ Top secret □ Secret □ Internal information ■ Open

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Fixed Resolution Output of Weston Desktop

Enter the ls/sys/class/DRM command to view the display device

View supported resolution.

Modify /etc/xdg/weston/weston.ini.

[output]
name=HDMI-A-1 //corresponds to the above list, with card0- removed
mode=1280x960 ///valid resolution supported by the screen
scale=1 //zoom factor, which must be an integer multiple

English Translation:

1. Forced HDMI Resolution Output without Reading EDID**

1.1 Modification Approach**

In U-Boot, enable the HDMI screen as the display output.
Modify the file OK3568-linux-source/kernel/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c:
- Add edid = NULL;
- Modify the parameters in the dw_hdmi_default_modes array.
If the required resolution parameters are not available in the dw_hdmi_default_modes array, you can refer to the OK3568-linux-source/kernel/drivers/gpu/drm/drm_edid.c file to find the required parameters and add them to the array in the same format.

1.2 Modification Method

Source file location: kernel/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c

static int dw_hdmi_connector_get_modes(struct drm_connector *connector)
{
    struct dw_hdmi *hdmi = container_of(connector, struct dw_hdmi,
                                        connector);
    --------Some code has been omitted-------
        edid = drm_get_edid(connector, hdmi->ddc);
//Don't read the current edid
    	edid = NULL;
    if (edid) {
        dev_dbg(hdmi->dev, "got edid: width[%d] x height[%d]\n",
                edid->width_cm, edid->height_cm);
        --------Some code has been omitted-------
            kfree(edid);
    } else {
        hdmi->support_hdmi = true;
        ...

//Keep only the desired resolution in dw_hdmi_default_modes
static const struct drm_display_mode dw_hdmi_default_modes[] = {
    /* 108 - 1920x1080@60Hz */
    { DRM_MODE("1920x1080", DRM_MODE_TYPE_DRIVER, 148500, 1920, 2008,
   2052, 2200, 0, 1080, 1084, 1089, 1125, 0,
   DRM_MODE_FLAG_NHSYNC | DRM_MODE_FLAG_NVSYNC), 
     .vrefresh = 60, .picture_aspect_ratio = HDMI_PICTURE_ASPECT_64_27, }, 
                +/* 
	4 - 1280x720@60Hz 16:9 
	{ DRM_MODE("1280x720", DRM_MODE_TYPE_DRIVER, 74250, 1280, 1390,
		   1430, 1650, 0, 720, 725, 730, 750, 0,
		   DRM_MODE_FLAG_PHSYNC | DRM_MODE_FLAG_PVSYNC),
	  .vrefresh = 60, .picture_aspect_ratio = HDMI_PICTURE_ASPECT_16_9, },
	 16 - 1920x1080@60Hz 16:9 

	--------Some code has been omitted-------

	 2 - 720x480@60Hz 4:3 
	{ 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, },
+*/
                };

Use ./build.sh kernel to compile the kernel separately and generate the /kernel/boot.img file. Then flash only the boot.img file.

Note: Some users have reported that after fixing the HDMI resolution using this method, the screen colors may appear different, and this issue may be screen-specific (i.e., certain screens may not fully comply with the setting). However, most users should be able to use this method normally.