On Thu, 10 Apr 2014, Daniel Vetter <daniel@xxxxxxxx> wrote: > On Thu, Apr 10, 2014 at 12:06:15PM +0530, Arun Chandran wrote: >> I have connected only a DP monitor on Bayley Bay platform and booting >> ubuntu 13.10 with the kernel >> http://cgit.freedesktop.org/drm-intel/log/?h=drm-intel-fixes. >> >> I am experimenting with the HPD feature of display port with debug >> messages enabled. (drm.debug=0xe). >> >> When I plug in/out DP cable I am able to see the below kernel messages >> and ubuntu desktop is displayed on the DP monitor >> >> ############################## >> >> >> root@arun-valley-view:~# uname -a >> Linux arun-valley-view 3.14.0-00528-g67e9d82 #34 SMP PREEMPT Wed Apr 9 >> 18:48:30 IST 2014 i686 i686 i686 GNU/Linux >> >> root@arun-valley-view:~# dmesg -c >> >> [ 1028.506188] [drm:intel_hpd_irq_handler] hotplug event received, >> stat 0x00100000 >> [ 1028.506217] [drm:intel_hpd_irq_handler] Received HPD interrupt on >> PIN 5 - cnt: 0 >> [ 1028.513858] [drm:i915_hotplug_work_func] running encoder hotplug functions >> [ 1028.513880] [drm:i915_hotplug_work_func] Connector eDP-1 (pin 5) >> received hotplug event. >> [ 1028.513896] [drm:i915_hotplug_work_func] Connector HDMI-A-2 (pin 5) >> received hotplug event. >> [ 1028.513913] [drm:_edp_panel_vdd_on] Turning eDP VDD on >> [ 1028.513931] [drm:_edp_panel_vdd_on] PP_STATUS: 0x80000008 >> PP_CONTROL: 0xabcd000f >> [ 1028.515064] [drm:intel_dp_get_dpcd] DPCD: 11 0a 84 01 01 00 01 80 >> 02 00 00 00 00 00 00 >> [ 1028.516563] [drm:intel_dp_check_link_status] TMDS-22: channel EQ >> not ok, retraining >> [ 1028.530884] [drm:intel_dp_set_signal_levels] Using signal levels 00000000 >> [ 1028.546113] [drm:intel_dp_set_signal_levels] Using signal levels 00000000 >> [ 1028.547233] [drm:intel_dp_start_link_train] clock recovery OK >> [ 1028.548711] [drm:intel_dp_complete_link_train] Channel EQ done. DP >> Training successful >> [ 1028.549264] [drm:intel_dp_detect] [CONNECTOR:23:eDP-1] >> [ 1028.549761] [drm:intel_dp_probe_oui] Sink OUI: 00e04c >> [ 1028.550262] [drm:intel_dp_probe_oui] Branch OUI: 000000 >> [ 1028.550343] [drm:intel_hdmi_detect] [CONNECTOR:21:HDMI-A-2] >> [ 1028.550595] [drm:gmbus_xfer] GMBUS [i915 gmbus dpc] NAK for addr: 0050 r(1) >> [ 1028.550611] [drm:drm_do_probe_ddc_edid] drm: skipping non-existent >> adapter i915 gmbus dpc >> >> ################################## >> >> After booting I am executing the below steps >> >> 1) unplug DP cable. >> >> 2) Mask the pin 18 (HPD) of DP cable using a paper strip then connect it >> back >> I have checked the dmesg output and the there is no messages related to >> HPD. So kernel is >> unaware that I have connected a DP monitor >> >> But still I see ubuntu desktop coming on the DP monitor. This means kernel >> does not stop pumping display data after step 1. >> >> Is this the right behavior? . When kernel knows that the last existing >> display is removed (via the HPD feature) it can save power by stopping the >> data output to DP monitor (or shutting down the DP hardware related part.) >> >> Does anybody knows how to use the HPD feature to save power? Or anybody has >> done this before? > > Yes, this is expected behaviour. Userspace asked the kernel to shovel > pixels to the DP screen, the kernel obeyed. If you want to kill the pipe > when unplugged, you need to make that policy decision in userspace. Hmm, in my reply I was assuming this had happened. The dmesgs would confirm. Jani. > > This is similar to how dpms off is driven by userspace and not the kernel. > -Daniel > -- > Daniel Vetter > Software Engineer, Intel Corporation > +41 (0) 79 365 57 48 - http://blog.ffwll.ch > _______________________________________________ > Intel-gfx mailing list > Intel-gfx@xxxxxxxxxxxxxxxxxxxxx > http://lists.freedesktop.org/mailman/listinfo/intel-gfx -- Jani Nikula, Intel Open Source Technology Center _______________________________________________ Intel-gfx mailing list Intel-gfx@xxxxxxxxxxxxxxxxxxxxx http://lists.freedesktop.org/mailman/listinfo/intel-gfx
