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  1. 1. How does xrandr get modes

X Resize and Rotate, is a extension for X server. xrandr is a tool of x11-xserver-utils.

How does xrandr get modes

  • modes indicates the resolution and refreshing for a monitor.

  • xinit or startx to start X server

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    $ xrandr
    or
    $ xrandr -q
    Screen 0: minimum 320 x 200, current 1920 x 1200, maximum 16384 x 16384
    VGA-0 connected 1920x1200+0+0 (normal left inverted right x axis y axis) 518mm x 324mm
       1920x1200      60.0*+
       1600x1200      60.0
       1280x1024      75.0     60.0
       1152x864       75.0
       1024x768       75.1     60.0
       800x600        75.0     60.3
       640x480        75.0     60.0
       720x400        70.1
    DisplayPort-0 disconnected (normal left inverted right x axis y axis)
    HDMI-A-0 disconnected (normal left inverted right x axis y axis)

  • The basic process of getting modes

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    xrandr -> X server(xrandr extension) -> libdrm -> kernel(DRM) -> get EDID from the monitor

  • Code path

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    --------------------------------------------------
    xrandr

      main() [xrandr.c]
      {
        /* to show mode name, such as 1920x1200 */
        jmode = find_mode_by_xid (output_info->modes[j]);
        printf (" ");
        printf ("  %-12s", jmode->name);
        ...

        /* If the name is same, continue
         * There is 12 modes in the mode list, skipping the mode with same name
         **/
        for (k = j; k < output_info->nmode; k++)
        {
            ...
            if (strcmp (jmode->name, kmode->name) != 0) continue;
            ...
        }
      }
      -> get_screen()
         -> XRRGetScreenResourcesCurrent()
            or
            XRRGetScreenResources()

    --------------------------------------------------
    X server

      get the command from ProcRandrVector[] [randr/rrdispatch.c]
      ProcRRGetScreenResources() [randr/rrscreen.c]
        rrGetScreenResources()
          RRGetInfo() [randr/rrinfo.c]
            *pScrPriv->rrGetInfo()
            It's xf86RandR12GetInfo12() [hw/xfree86/modes/xf86RandR12.c]
              xf86ProbeOutputModes() [hw/xfree86/modes/xf86Crtc.c]
                output_modes = (*output->funcs->get_modes) (output); [hw/xfree86/modes/xf86Crtc.c]

            ddx
            ------------------------------------------
                .get_modes = drmmode_output_get_modes in ddx
                  {
                  mode is converted from kmode via drmmode_ConvertFromKMode(, &koutput->modes[i], )
                  drmModeConnectorPtr koutput = drmmode_output->mode_output;
                  drmmode_output_private_ptr drmmode_output = output->driver_private;

                  drmmode_output->mode_output = koutput; in drmmode_output_init()
                  output->driver_private = drmmode_output
                  koutput = drmModeGetConnector();
                  }

    --------------------------------------------------
    libdrm

      drmModeGetConnector() [xf86drmMode.c]
        _drmModeGetConnector()
          drmIoctl(fd, DRM_IOCTL_MODE_GETCONNECTOR, &conn)

    --------------------------------------------------
    kernel(DRM)

      drm_mode_getconnector() [drivers/gpu/drm/drm_crtc.c]
        connector->funcs->fill_modes()
        it's drm_helper_probe_single_connector_modes() [drivers/gpu/drm/drm_probe_helper.c]
          drm_helper_probe_single_connector_modes_merge_bits()
            drm_load_edid_firmware(connector);
            count = (*connector_funcs->get_modes)(connector);
            it's amdgpu_connector_dp_get_modes() [drivers/gpu/drm/amd/amdgpu/amdgpu_connectors.c]
              amdgpu_connector_encoder_get_dp_bridge_encoder_id() to setup ddc on the bridge
              amdgpu_connector_get_edid()
              amdgpu_connector_ddc_get_modes()
                drm_add_edid_modes() add modes from EDID data [drivers/gpu/drm/drm_edid.c]
                  add_detailed_modes()
                  add_cvt_modes()
                  ...
Contents
  1. 1. How does xrandr get modes