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

From: Jani Nikula
Date: Mon Aug 13 2012 - 06:18:57 EST


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

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

drm/i915: reenable gmbus on gen3+ again

and

commit 0fb3f969c8683505fb7323c06bf8a999a5a45a15
Author: Daniel Vetter <daniel.vetter@xxxxxxxx>
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@xxxxxxxxx>
Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=45881
Signed-off-by: Jani Nikula <jani.nikula@xxxxxxxxx>
---
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

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