From 8d16f258217f2f583af1fd57c5144aa4bbe73e48 Mon Sep 17 00:00:00 2001 From: Jani Nikula Date: Fri, 20 Sep 2013 16:42:15 +0300 Subject: [PATCH] drm/i915/dp: increase i2c-over-aux retry interval on AUX DEFER There is no clear cut rules or specs for the retry interval, as there are many factors that affect overall response time. Increase the interval, and even more so on branch devices which may have limited i2c bit rates. Signed-off-by: Jani Nikula Reference: https://bugs.freedesktop.org/show_bug.cgi?id=60263 Tested-by: Nicolas Suzor Reviewed-by: Todd Previte Cc: stable@vger.kernel.org Signed-off-by: Daniel Vetter --- drivers/gpu/drm/i915/intel_dp.c | 13 ++++++++++++- 1 file changed, 12 insertions(+), 1 deletion(-) diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c index 2151d13772b8..79c14e298ba6 100644 --- 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", -- GitLab