[PATCH 2/2] drm/i915: fall back to bit-banging if GMBUS fails in CRT EDID reads

[Jani Nikula]

GMBUS was enabled over bit-banging as the default in commits:

commit c3dfefa0a6d235bd465309e12f4c56ea16e71111
Author: Daniel Vetter <daniel.vetter at ffwll.ch>
Date:   Tue Feb 14 22:37:25 2012 +0100

    drm/i915: reenable gmbus on gen3+ again

and

commit 0fb3f969c8683505fb7323c06bf8a999a5a45a15
Author: Daniel Vetter <daniel.vetter at ffwll.ch>
Date:   Fri Mar 2 19:38:30 2012 +0100

    drm/i915: enable gmbus on gen2

Unfortunately, GMBUS seems to fail on some CRT displays. Add a bit-banging
fallback to CRT EDID reads.

LKML-Reference: <201207251020.47637.maciej.rutecki at gmail.com>
Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=45881
Signed-off-by: Jani Nikula <jani.nikula at intel.com>
---
 drivers/gpu/drm/i915/intel_crt.c |   36 +++++++++++++++++++++++++++++++++---
 1 file changed, 33 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_crt.c b/drivers/gpu/drm/i915/intel_crt.c
index bc5e2c9..80bf311 100644
--- a/drivers/gpu/drm/i915/intel_crt.c
+++ b/drivers/gpu/drm/i915/intel_crt.c
@@ -328,6 +328,36 @@ static bool intel_crt_detect_hotplug(struct drm_connector 
*connector)
        return ret;
 }

+static struct edid *intel_crt_get_edid(struct drm_connector *connector,
+                               struct i2c_adapter *i2c)
+{
+       struct edid *edid;
+
+       edid = drm_get_edid(connector, i2c);
+
+       if (!edid && !intel_gmbus_is_forced_bit(i2c)) {
+               DRM_DEBUG_KMS("CRT GMBUS EDID read failed, retry using GPIO 
bit-banging\n");
+               intel_gmbus_force_bit(i2c, true);
+               edid = drm_get_edid(connector, i2c);
+               intel_gmbus_force_bit(i2c, false);
+       }
+
+       return edid;
+}
+
+/* local version of intel_ddc_get_modes() to use intel_crt_get_edid() */
+static int intel_crt_ddc_get_modes(struct drm_connector *connector,
+                               struct i2c_adapter *adapter)
+{
+       struct edid *edid;
+
+       edid = intel_crt_get_edid(connector, adapter);
+       if (!edid)
+               return 0;
+
+       return intel_connector_update_modes(connector, edid);
+}
+
 static bool intel_crt_detect_ddc(struct drm_connector *connector)
 {
        struct intel_crt *crt = intel_attached_crt(connector);
@@ -338,7 +368,7 @@ static bool intel_crt_detect_ddc(struct drm_connector 
*connector)
        BUG_ON(crt->base.type != INTEL_OUTPUT_ANALOG);

        i2c = intel_gmbus_get_adapter(dev_priv, dev_priv->crt_ddc_pin);
-       edid = drm_get_edid(connector, i2c);
+       edid = intel_crt_get_edid(connector, i2c);

        if (edid) {
                bool is_digital = edid->input & DRM_EDID_INPUT_DIGITAL;
@@ -546,13 +576,13 @@ static int intel_crt_get_modes(struct drm_connector 
*connector)
        struct i2c_adapter *i2c;

        i2c = intel_gmbus_get_adapter(dev_priv, dev_priv->crt_ddc_pin);
-       ret = intel_ddc_get_modes(connector, i2c);
+       ret = intel_crt_ddc_get_modes(connector, i2c);
        if (ret || !IS_G4X(dev))
                return ret;

        /* Try to probe digital port for output in DVI-I -> VGA mode. */
        i2c = intel_gmbus_get_adapter(dev_priv, GMBUS_PORT_DPB);
-       return intel_ddc_get_modes(connector, i2c);
+       return intel_crt_ddc_get_modes(connector, i2c);
 }

 static int intel_crt_set_property(struct drm_connector *connector,
-- 
1.7.9.5