i915: lvds panel always blank when booted with lid closed

From 250904ac95cda7630cdd8339724e3c8feceeb586 Mon Sep 17 00:00:00 2001

When I boot my Thinkpad T410 in a docking station with the lid closed, the lvds panel remains blank even when this output is active. This happens up to and including 3.5-rc2.

I've determined that this happens because lvds isn't being initialized by the bios when I boot this way, and booting with lvds_channel_mode=2 fixes the issue. I see that there's logic in is_dual_link_lvds() intended to detect this situation, but it's failing because the T410 has the LVDS_PIPEB_SELECT bit set. The simple patch below fixes my machine by masking off this bit when determining whether or not lvds was initialized by the bios.

I'm not sure though whether or not it's correct to expect that this bit might be set when lvds hasn't been initialized. The alternative seems to be quirking this machine as is done for some Macbooks. What is the correct solution?

Thanks,
Seth

From 250904ac95cda7630cdd8339724e3c8feceeb586 Mon Sep 17 00:00:00 2001
From: Seth Forshee <[email protected]>
Date: Tue, 12 Jun 2012 16:52:14 -0500
Subject: [PATCH] drm/i915: ignore LVDS_PIPEB_SELECT when checking for LVDS
register initialization

The Lenovo Thinkpad T410 has this bit set in the LVDS register when booted with the lid closed, even though the LVDS hasn't really been initialized. Ignore this bit so that the VBT value will be used instead.

Signed-off-by Seth Forshee <[email protected]>

---
 drivers/gpu/drm/i915/intel_display.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

drivers/gpu/drm/i915/intel_display.c +1 -1

index e0aa064..f81f249 100644
@@ -434,7 +434,7 @@ static bool is_dual_link_lvds(struct drm_i915_private *dev_priv,
 		 * register is uninitialized.
 		 */
 		val = I915_READ(reg);
-		if (!(val & ~LVDS_DETECTED))
+		if (!(val & ~(LVDS_PIPEB_SELECT | LVDS_DETECTED)))
 			val = dev_priv->bios_lvds_val;
 		dev_priv->lvds_val = val;
 	}

The Lenovo Thinkpad T410 has the LVDS_PIPEB_SELECT bit set in the LVDS register when booted with the lid closed, even though the LVDS hasn't really been initialized. Ignore this bit so that the VBT value will be used instead.

Signed-off-by Seth Forshee <[email protected]>

---
 drivers/gpu/drm/i915/intel_display.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

drivers/gpu/drm/i915/intel_display.c +1 -1

index e0aa064..ae17526 100644
@@ -434,7 +434,7 @@ static bool is_dual_link_lvds(struct drm_i915_private *dev_priv,
 		 * register is uninitialized.
 		 */
 		val = I915_READ(reg);
-		if (!(val & ~LVDS_DETECTED))
+		if (!(val & ~(LVDS_PIPE_MASK | LVDS_DETECTED)))
 			val = dev_priv->bios_lvds_val;
 		dev_priv->lvds_val = val;
 	}

Signature · 1 line

1.7.9.5

Quoted 6 lines · Seth Forshee

The Lenovo Thinkpad T410 has the LVDS_PIPEB_SELECT bit set in the LVDS register when booted with the lid closed, even though the LVDS hasn't really been initialized. Ignore this bit so that the VBT value will be used instead.

Signed-off-by Seth Forshee <[email protected]>

Queued for -next, thanks for the patch. Chris had some reservations about the sanity of this patch, but given that it works around bios-insanity I'm gonna just take this chance to stab myself with lvds-machines blowing up left and right ;-)

Quoted 11 lines · Daniel Vetter

Quoted 6 lines · Seth Forshee

The Lenovo Thinkpad T410 has the LVDS_PIPEB_SELECT bit set in the LVDS register when booted with the lid closed, even though the LVDS hasn't really been initialized. Ignore this bit so that the VBT value will be used instead.

Signed-off-by Seth Forshee <[email protected]>

Queued for -next, thanks for the patch. Chris had some reservations about the sanity of this patch, but given that it works around bios-insanity I'm gonna just take this chance to stab myself with lvds-machines blowing up left and right ;-)

Let's hope that doesn't happen ;)

I do find myself wondering though whether it might be better to prefer the value from the VBT whenever there's one available, and only rely on the actual register value as a fallback, since the bios can't be trusted to initialize the register. I'm pretty ignorant about all this graphics stuff though; I assume there's a reason it isn't done this way?