drm/i915/dp: increase i2c-over-aux retry interval on AUX DEFER

[cascardo/linux.git] / drivers / gpu / drm / i915 / intel_dp.c

diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
index 2151d13..79c14e2 100644 (file)
--- a/drivers/gpu/drm/i915/intel_dp.c
+++ b/drivers/gpu/drm/i915/intel_dp.c
@@ -588,7 +588,18 @@ intel_dp_i2c_aux_ch(struct i2c_adapter *adapter, int mode,
                        DRM_DEBUG_KMS("aux_ch native nack\n");
                        return -EREMOTEIO;
                case AUX_NATIVE_REPLY_DEFER:
-                       udelay(100);
+                       /*
+                        * For now, just give more slack to branch devices. We
+                        * could check the DPCD for I2C bit rate capabilities,
+                        * and if available, adjust the interval. We could also
+                        * be more careful with DP-to-Legacy adapters where a
+                        * long legacy cable may force very low I2C bit rates.
+                        */
+                       if (intel_dp->dpcd[DP_DOWNSTREAMPORT_PRESENT] &
+                           DP_DWN_STRM_PORT_PRESENT)
+                               usleep_range(500, 600);
+                       else
+                               usleep_range(300, 400);
                        continue;
                default:
                        DRM_ERROR("aux_ch invalid native reply 0x%02x\n",