hi all, when I run modetest process in libdrm to test our drm module, I find a strange problem: The test successfully opened /dev/dri/card0 (major:226 minor:0) device by using module name. but the returned message about crtc, encoder and connector are all empty. I confirm the num of them is one when our drm device driver register in kernel. So I track the kernel and find here:

drivers/gpu/drm/drm_crtc.c

1806 if (!drm_is_primary_client(file_priv)) { 1807 1808 mode_group = NULL; 1809 list_for_each(lh, &dev->mode_config.crtc_list) 1810 crtc_count++; 1811 1812 list_for_each(lh, &dev->mode_config.connector_list) 1813 connector_count++; 1814 1815 list_for_each(lh, &dev->mode_config.encoder_list) 1816 encoder_count++; 1817 } else { 1818 1819 mode_group = &file_priv->master->minor->mode_group; 1820 crtc_count = mode_group->num_crtcs; 1821 connector_count = mode_group->num_connectors; 1822 encoder_count = mode_group->num_encoders; 1823 }

The device we opened with type of DRM_MINOR_LEGACY, so here come into else branch. The description of drm_mode_group is that struct drm_mode_group - group of mode setting resources for potential sub-grouping, and the note in drm_crtc.h also said :

943 * Currently this simply tracks the global mode setting state. But in the 944 * future it could allow groups of objects to be set aside into independent 945 * control groups for use by different user level processes (e.g. two X servers 946 * running simultaneously on different heads, each with their own mode 947 * configuration and freedom of mode setting).

I doubt the empty result has some relations with it, so I continue to track the kernel in function drm_open, and I find mode_group lies in drm_minor, whick can be found by inode in function drm_open. But when we create a crtc, encoder or connector, we do nothing to mode_group, just initializing it when drm_core register. Can you help me and give me some advice?

regards, Yunlei He