From mboxrd@z Thu Jan  1 00:00:00 1970
From: Egbert Eich <eich@freedesktop.org>
Subject: Re: [PATCH] drm/i915: force full modeset if the
 connector is in DPMS OFF mode
Date: Fri, 3 May 2013 19:40:08 +0200
Message-ID: <20130503174008.GF17947@debian>
References: <1367580129-6681-1-git-send-email-imre.deak@intel.com>
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To: Imre Deak <imre.deak@intel.com>
Cc: intel-gfx@lists.freedesktop.org
List-Id: intel-gfx@lists.freedesktop.org

On Fri, May 03, 2013 at 02:22:09PM +0300, Imre Deak wrote:
> Currently the driver's assumed behavior for a modeset with an attached
> FB is that the corresponding connector will be switched to DPMS ON mode
> if it happened to be in DPMS OFF (or another power save mode). This
> wasn't enforced though if only the FB changed, everything else (format,
> connector etc.) remaining the same. In this case we only set the new FB
> base and left the connector in the old power save mode.
> 
> Fix this by forcing a full modeset whenever there is an attached FB and
> any affected connector is in a power save mode.
> 
> Signed-off-by: Imre Deak <imre.deak@intel.com>

[..]

> @@ -8397,8 +8412,12 @@ intel_set_config_compute_mode_changes(struct drm_mode_set *set,
>  		} else if (set->fb->pixel_format !=
>  			   set->crtc->fb->pixel_format) {
>  			config->mode_changed = true;
> -		} else
> +		} else if (crtc_connector_off(set->crtc, *set->connectors,
> +					      set->num_connectors)) {
> +			config->mode_changed = true;
> +		} else {
>  			config->fb_changed = true;
> +		}
>  	}
>  
>  	if (set->fb && (set->x != set->crtc->x || set->y != set->crtc->y))

On https://bugs.freedesktop.org/show_bug.cgi?id=64178
I had a similar problem for which I found a very similar 'workaround':

Assuming the Xserver is displaying a mode a on output A, doing a:

xrandr --output A --off
xrandr --output A --mode a

will not light up the screen.

This all sounds quite similar, to the issues describe by this patch,
however the patch as is will not fix this issue: With this setup the
fb does not change. The crtc_connector_off() test however only runs if
set->crtc->fb != set->fb is true.

Thus the connector_off() test needs to happen before:

-       if (set->crtc->fb != set->fb) {
+       if (set->connectors != NULL && 
+           connector_off(set->crtc, *set->connectors,
+                         set->num_connectors)) {
+                       config->mode_changed = true;
+       } else if (set->crtc->fb != set->fb) {

Mind the test for set->connectors != NULL as now the connectors list
may be empty.

Cheers,
	Egbert.