[Intel-gfx] [PATCH] xf86-video-intel: change order of DPMS operations

[Simon Que]

The operations when setting dpms on should be in the order opposite
of what's done when setting dpms off.

This is because of potentially conflicting effects:
~ drmModeConnectoSetProperty() enables/disables the backlight driver.
Some backlight drivers such as intel_backlight set the backlight to 0
when disabled and to max when enabled.
~ intel_output_dpms_backlight() saves the backlight value when turning
DPMS off and restores it when turning DPMS on.

Here's the current order of operations:

xset dpms force off (backlight is nonzero)
   drmModeConnectoSetProperty(DPMSModeOff)
      kernel: disable backlight, backlight=0
   intel_output_dpms_backlight(DPMSModeOff)
      save backlight value (0) <-- it has been set to 0 by kernel
      set backlight to 0

xset dpms force on
   drmModeConnectoSetProperty(DPMSModeOn)
      kernel: enable backlight, backlight=max
   intel_output_dpms_backlight(DPMSModeOn)
      set backlight to saved value (0)

The correct way to do this would be to reverse the operations during
xset dpms force off:
   intel_output_dpms_backlight(DPMSModeOff)
      save backlight value (nonzero)
      set backlight to 0
   drmModeConnectoSetProperty(DPMSModeOff)
      kernel: enable backlight, backlight=0

This restores the saved nonzero backlight value during the force on.

Signed-off-by: Simon Que <sque at chromium.org>
---
 src/intel_display.c |   12 +++++++++---
 1 files changed, 9 insertions(+), 3 deletions(-)

diff --git a/src/intel_display.c b/src/intel_display.c
index 2183f4d..2a989d1 100644
--- a/src/intel_display.c
+++ b/src/intel_display.c
@@ -944,13 +944,19 @@ intel_output_dpms(xf86OutputPtr output, int dpms)
 			continue;
 
 		if (!strcmp(props->name, "DPMS")) {
+			/* Make sure to reverse the order between on and off. */
+			if (dpms == DPMSModeOff)
+				intel_output_dpms_backlight(output,
+							    intel_output->dpms_mode,
+							    dpms);
 			drmModeConnectorSetProperty(mode->fd,
 						    intel_output->output_id,
 						    props->prop_id,
 						    dpms);
-			intel_output_dpms_backlight(output,
-						      intel_output->dpms_mode,
-						      dpms);
+			if (dpms != DPMSModeOff)
+				intel_output_dpms_backlight(output,
+							    intel_output->dpms_mode,
+							    dpms);
 			intel_output->dpms_mode = dpms;
 			drmModeFreeProperty(props);
 			return;
-- 
1.7.3.1