diff options
authorJani Nikula <jani.nikula@intel.com>2015-06-02 19:21:15 +0300
committerJani Nikula <jani.nikula@intel.com>2015-06-09 10:34:15 +0300
commit3f5f1554ee715639e78d9be87623ee82772537e0 (patch)
parent8ce7da474f3063f57ac446eb428945a9852e102d (diff)
drm/i915: Fix DDC probe for passive adaptersdrm-intel-fixes-2015-06-11
Passive DP->DVI/HDMI dongles on DP++ ports show up to the system as HDMI devices, as they do not have a sink device in them to respond to any AUX traffic. When probing these dongles over the DDC, sometimes they will NAK the first attempt even though the transaction is valid and they support the DDC protocol. The retry loop inside of drm_do_probe_ddc_edid() would normally catch this case and try the transaction again, resulting in success. That, however, was thwarted by the fix for [1]: commit 9292f37e1f5c79400254dca46f83313488093825 Author: Eugeni Dodonov <eugeni.dodonov@intel.com> Date: Thu Jan 5 09:34:28 2012 -0200 drm: give up on edid retries when i2c bus is not responding This added code to exit immediately if the return code from the i2c_transfer function was -ENXIO in order to reduce the amount of time spent in waiting for unresponsive or disconnected devices. That was possible because the underlying i2c bit banging algorithm had retries of its own (which, of course, were part of the reason for the bug the commit fixes). Since its introduction in commit f899fc64cda8569d0529452aafc0da31c042df2e Author: Chris Wilson <chris@chris-wilson.co.uk> Date: Tue Jul 20 15:44:45 2010 -0700 drm/i915: use GMBUS to manage i2c links we've been flipping back and forth enabling the GMBUS transfers, but we've settled since then. The GMBUS implementation does not do any retries, however, bailing out of the drm_do_probe_ddc_edid() retry loop on first encounter of -ENXIO. This, combined with Eugeni's commit, broke the retry on -ENXIO. Retry GMBUS once on -ENXIO on first message to mitigate the issues with passive adapters. This patch is based on the work, and commit message, by Todd Previte <tprevite@gmail.com>. [1] https://bugs.freedesktop.org/show_bug.cgi?id=41059 v2: Don't retry if using bit banging. v3: Move retry within gmbux_xfer, retry only on first message. v4: Initialize GMBUS0 on retry (Ville). v5: Take index reads into account (Ville). Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=85924 Cc: Todd Previte <tprevite@gmail.com> Cc: stable@vger.kernel.org Tested-by: Oliver Grafe <oliver.grafe@ge.com> (v2) Tested-by: Jim Bride <jim.bride@linux.intel.com> Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com> Signed-off-by: Jani Nikula <jani.nikula@intel.com>
1 files changed, 17 insertions, 3 deletions
diff --git a/drivers/gpu/drm/i915/intel_i2c.c b/drivers/gpu/drm/i915/intel_i2c.c
index 56e437e31580..ae628001fd97 100644
--- a/drivers/gpu/drm/i915/intel_i2c.c
+++ b/drivers/gpu/drm/i915/intel_i2c.c
@@ -435,7 +435,7 @@ gmbus_xfer(struct i2c_adapter *adapter,
struct intel_gmbus,
struct drm_i915_private *dev_priv = bus->dev_priv;
- int i, reg_offset;
+ int i = 0, inc, try = 0, reg_offset;
int ret = 0;
@@ -448,12 +448,14 @@ gmbus_xfer(struct i2c_adapter *adapter,
reg_offset = dev_priv->gpio_mmio_base;
I915_WRITE(GMBUS0 + reg_offset, bus->reg0);
- for (i = 0; i < num; i++) {
+ for (; i < num; i += inc) {
+ inc = 1;
if (gmbus_is_index_read(msgs, i, num)) {
ret = gmbus_xfer_index_read(dev_priv, &msgs[i]);
- i += 1; /* set i to the index of the read xfer */
+ inc = 2; /* an index read is two msgs */
} else if (msgs[i].flags & I2C_M_RD) {
ret = gmbus_xfer_read(dev_priv, &msgs[i], 0);
} else {
@@ -525,6 +527,18 @@ clear_err:
adapter->name, msgs[i].addr,
(msgs[i].flags & I2C_M_RD) ? 'r' : 'w', msgs[i].len);
+ /*
+ * Passive adapters sometimes NAK the first probe. Retry the first
+ * message once on -ENXIO for GMBUS transfers; the bit banging algorithm
+ * has retries internally. See also the retry loop in
+ * drm_do_probe_ddc_edid, which bails out on the first -ENXIO.
+ */
+ if (ret == -ENXIO && i == 0 && try++ == 0) {
+ DRM_DEBUG_KMS("GMBUS [%s] NAK on first message, retry\n",
+ adapter->name);
+ goto retry;
+ }
goto out;

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