OK3568 4.19.206 Buildroot Fixed Resolution Output

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Copyright

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Fixed Resolution Output

Fixed Resolution Output for Weston Desktop

1. Enter ls /sys/class/drm to check display devices.

2. View supported resolutions.

Modify the file /etc/xdg/weston/weston.ini:

[output]
name=HDMI-A-1 //Corresponding to the above list, remove card0-
mode=1280x960 //A valid resolution supported by the screen
scale=1 //Zoom factor, which should be an integer multiple

Forced HDMI Resolution Output Without Reading EDID

Modification Method

Enable HDMI screen output in U-Boot.

Modify Ok3568-linux-source/kernel/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c:

Add edid = NULL.

Adjust parameters in the dw_hdmi_default_modes array.

If the required resolution parameters are not in dw_hdmi_default_modes, search OK3568-linux-source/kernel/drivers/gpu/drm/drm_edid.c for corresponding parameters and add them to the array in the correct format.

Modification Steps

1. Source 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);
    --------Omit some codes-------
        edid = drm_get_edid(connector, hdmi->ddc);
//Do not read current edid
    	edid = NULL;
    if (edid) {
        dev_dbg(hdmi->dev, "got edid: width[%d] x height[%d]\n",
                edid->width_cm, edid->height_cm);
        --------Omit some codes-------
            kfree(edid);
    } else {
        hdmi->support_hdmi = true;
        ...

//Keep only the desired resolution in the 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 

	--------Omit some codes-------

	 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, },
+*/
                };

2. Compile separately with the./build. sh kernel to generate the/kernel/boot. img file;

3. Flash the boot.img file separately.

Note: Some users have reported color discrepancies or screen compatibility issues (known as “picky screen” phenomenon) after forcing the HDMI resolution via the method described above. However, the majority of users can still use it normally.