drm/i915: disable sdvo hotplug on i945g/gm

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 <simon.farnsworth@onelan.co.uk>
Date:   Wed Sep 21 17:13:30 2011 +0100

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

Cc: stable@kernel.org
Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=38442
Reported-and-tested-by: Dominik Köppl <dominik@devwork.org>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-Off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

diff --git a/drivers/gpu/drm/i915/intel_sdvo.c b/drivers/gpu/drm/i915/intel_sdvo.c
index 232d77d..ae5e748 100644 (file)
--- a/drivers/gpu/drm/i915/intel_sdvo.c
+++ b/drivers/gpu/drm/i915/intel_sdvo.c
@@ -1220,8 +1220,14 @@ static bool intel_sdvo_get_capabilities(struct intel_sdvo *intel_sdvo, struct in
 
 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];
 }