Re: 2.6.38-rc3-git1: Reported regressions 2.6.36 -> 2.6.37

[Linus Torvalds]

On Thu, Feb 3, 2011 at 1:56 PM, Carlos Mafra <crmafra2@xxxxxxxxx> wrote:
>>
>> I added https://bugzilla.kernel.org/show_bug.cgi?id=24982 to the list of
>> post-2.6.36 regressions for further tracking.
>
> I also tested on 2.6.38-rc3+ now and the issue is not solved,
> just like Takashi expected.

Hmm. That commit (bf9dc102e284) still reverts cleanly.

Keith, Dave, should we just revert it? It's definitely a regression,
and we do _not_ allow "fixes" to one thing that just causes a
regression to another.

Quite frankly, I think it's totally wrong to just blindly set DPMS
status to ON like that. It's as wrong as it was to leave it off, and
the regressions reported are basically mirror images of the exact same
bug that that commit tried to fix.

IOW, the commit message says:

    When setting a new crtc configuration, force the DPMS state of all
    connectors to ON. Otherwise, they'll be left at OFF and a future mode set
    that disables the specified connector will not turn the connector off.

but setting it to ON doesn't actually _fix_ anything, because you just
get the exact same issue in reverse, ie you just get

   .. and a future mode set  that ENables the specified connector will
    not turn the connector ON.

instead. Which is exactly what Carlos and Takashi are reporting.

Maybe the right thing to do is to set it to 'unknown', something like this.

TOTALLY UNTESTED!

                          Linus
 drivers/gpu/drm/drm_crtc_helper.c |    6 +++---
 include/drm/drm_mode.h            |    1 +
 2 files changed, 4 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/drm_crtc_helper.c b/drivers/gpu/drm/drm_crtc_helper.c
index 952b3d4..7f585ed 100644
--- a/drivers/gpu/drm/drm_crtc_helper.c
+++ b/drivers/gpu/drm/drm_crtc_helper.c
@@ -681,11 +681,11 @@ int drm_crtc_helper_set_config(struct drm_mode_set *set)
 			goto fail;
 		}
 	}
-	DRM_DEBUG_KMS("Setting connector DPMS state to on\n");
+	DRM_DEBUG_KMS("Setting connector DPMS state to 'unknown'\n");
 	for (i = 0; i < set->num_connectors; i++) {
-		DRM_DEBUG_KMS("\t[CONNECTOR:%d:%s] set DPMS on\n", set->connectors[i]->base.id,
+		DRM_DEBUG_KMS("\t[CONNECTOR:%d:%s] set DPMS 'unknown'\n", set->connectors[i]->base.id,
 			      drm_get_connector_name(set->connectors[i]));
-		set->connectors[i]->dpms = DRM_MODE_DPMS_ON;
+		set->connectors[i]->dpms = DRM_MODE_DPMS_UNKNOWN;
 	}
 
 	kfree(save_connectors);
diff --git a/include/drm/drm_mode.h b/include/drm/drm_mode.h
index 0fc7397..4b5144c 100644
--- a/include/drm/drm_mode.h
+++ b/include/drm/drm_mode.h
@@ -59,6 +59,7 @@
 
 /* DPMS flags */
 /* bit compatible with the xorg definitions. */
+#define DRM_MODE_DPMS_UNKNOWN	(-1)
 #define DRM_MODE_DPMS_ON	0
 #define DRM_MODE_DPMS_STANDBY	1
 #define DRM_MODE_DPMS_SUSPEND	2