[ 06/52] drm/i915: disable sdvo hotplug on i945g/gm

3.3-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Daniel Vetter <redacted>

commit 768b107e4b3be0acf6f58e914afe4f337c00932b upstream.

Chris Wilson dug out a hw erratum saying that there's noise on the
interrupt line on i945G chips. We also have a bug report from a i945GM
chip with an sdvo hotplug interrupt storm (and no apparent cause).

Play it safe and disable sdvo hotplug on all i945 variants.

Note that this is a regression that has been introduced in 3.1,
when we've enabled sdvo hotplug support with

commit cc68c81aed7d892deaf12d720d5455208e94cd0a
Author: Simon Farnsworth [off-list ref]
Date:   Wed Sep 21 17:13:30 2011 +0100

    drm/i915: Enable SDVO hotplug interrupts for HDMI and DVI

Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=38442
Reported-and-tested-by: Dominik K��ppl <redacted>
Reviewed-by: Chris Wilson <redacted>
Signed-Off-by: Daniel Vetter <redacted>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 drivers/gpu/drm/i915/intel_sdvo.c |    6 ++++++
 1 file changed, 6 insertions(+)

--- a/drivers/gpu/drm/i915/intel_sdvo.c
+++ b/drivers/gpu/drm/i915/intel_sdvo.c

@@ -1221,8 +1221,14 @@ static bool intel_sdvo_get_capabilities(
 
 static int intel_sdvo_supports_hotplug(struct intel_sdvo *intel_sdvo)
 {
+	struct drm_device *dev = intel_sdvo->base.base.dev;
 	u8 response[2];
 
+	/* HW Erratum: SDVO Hotplug is broken on all i945G chips, there's noise
+	 * on the line. */
+	if (IS_I945G(dev) || IS_I945GM(dev))
+		return false;
+
 	return intel_sdvo_get_value(intel_sdvo, SDVO_CMD_GET_HOT_PLUG_SUPPORT,
 				    &response, 2) && response[0];
 }