[PATCH] drm/crtc: fix connector reference counting mismatch in drm_crtc_helper_set_config

[Philipp Zabel]

Am Donnerstag, den 02.06.2016, 22:25 +0200 schrieb Daniel Vetter:
[...]
> >     [drm:drm_ioctl] pid=205, dev=0xe201, auth=1, DRM_IOCTL_MODE_SETCRTC
> >     [drm:drm_mode_setcrtc] [CRTC:24:crtc-0]
> >     [drm:drm_mode_setcrtc] [CONNECTOR:36:LVDS-1]

^ This is printed after each drm_connector_lookup call. The crtc_req
only contains connector 36, and only that one is looked up and gets its
refcount incremented to 2. The unrelated, unbound connector 34 is not
part of the request, doesn't get added to the drm_mode_set, and stays at
reference count 1.

> >     [drm:drm_crtc_helper_set_config] 
> >     [drm:drm_crtc_helper_set_config] [CRTC:24:c 13.982686] [drm:drm_mode_debug_printmodeline] Modeline 0:"" 0 0 0 0 0 0 0 0 0 0 0x0 0x0
> >     [drm:drm_mode_debug_printmodeline] Modeline 41:"1280x800" 60 71100 1280 1281 1439 1440 800 801 822 823 0x40 0x0
> >     [drm:drm_mode_object_reference] OBJ ID: 36 (2)
> >     [drm:drm_crtc_helper_set_config] encoder changed, full mode switch
> >     [drm:drm_crtc_helper_set_config] crtc changed, full mode switch
> >     [drm:drm_crtc_helper_set_config] [CONNECTOR:36:LVDS-1] to [CRtc-0]
> >     [drm:drm_crtc_helper_set_mode] [ENCODER:35:LVDS-35] set [MODE:41:1280x800]
> >     [drm:drm_calc_timestamping_constants] crtc 24: hwmode: htotal 1440, vtotal 823, vdisplay 800
> >     [drm:drm_calc_timestamping_constants] crtc 24: clock 71100 kHz framedur 16668354 linedur 20253
> >     [drm:drm_crtc_helper_set_config] Setting connector DPMS state to on
> >     [drm:drm_crtc_helper_set_config] 	[CONNECTOR:36:LVDS-1] set DPMS on
> >     [drm:drm_mode_object_unreference] OBJ ID: 34 (1)

^ And here the temporary copy of connector 34 gets its reference count
decremented to 0.

> The additional get/put I'm talking off happens in drm_mode_setcrtc (the
> get is hidden in drm_connector_lookup). Might be interesting to trace the
> refcount for each connector after each get and before each put.

drm_connector_lookup is not called for connector 34 if userspace just
requests to enable a single output on connector 36.

regards
Philipp