drm/i915/dp: Add workaround for spurious AUX timeouts/hotplugs on LTTPR links
To avoid AUX timeouts and subsequent spurious hotplug interrupts, make sure that the first DPCD access during detection is a read from an LTTPR register. Some ADLP DP link configuration at least with multiple LTTPRs expects the first DPCD access during the LTTPR/DPCD detection after hotplug to be a read from the LTTPR range starting with DP_LT_TUNABLE_PHY_REPEATER_FIELD_DATA_STRUCTURE_REV. The side effect of this read is to put each LTTPR into the LTTPR transparent or LTTPR non-transparent mode. The lack of the above read may leave some of the LTTPRs in non-LTTPR mode, while other LTTPRs in LTTPR transparent or LTTPR non-transparent mode (for instance LTTPRs after system suspend/resume that kept their mode from before suspend). Due to the different AUX timeouts the different modes imply, the DPCD access from a non-LTTPR range will timeout and lead to an LTTPR generated hotplug towards the source (which the LTTPR firmware uses to account for buggy TypeC adapters with a long wake-up delay). SYSCROS: 72939 v2: Keep DPCD read-out working on non-LTTPR platforms. v3: Summarize what and why the patch does at the beginning of the commit log. (Jani) Signed-off-by: Imre Deak <imre.deak@intel.com> Reviewed-by: Jani Nikula <jani.nikula@intel.com> Link: https://patchwork.freedesktop.org/patch/msgid/20220408224629.845887-1-imre.deak@intel.com
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@ -82,19 +82,8 @@ static bool intel_dp_read_lttpr_common_caps(struct intel_dp *intel_dp,
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const u8 dpcd[DP_RECEIVER_CAP_SIZE])
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{
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struct intel_encoder *encoder = &dp_to_dig_port(intel_dp)->base;
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struct drm_i915_private *i915 = to_i915(encoder->base.dev);
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int ret;
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if (intel_dp_is_edp(intel_dp))
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return false;
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/*
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* Detecting LTTPRs must be avoided on platforms with an AUX timeout
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* period < 3.2ms. (see DP Standard v2.0, 2.11.2, 3.6.6.1).
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*/
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if (DISPLAY_VER(i915) < 10 || IS_GEMINILAKE(i915))
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return false;
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ret = drm_dp_read_lttpr_common_caps(&intel_dp->aux, dpcd,
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intel_dp->lttpr_common_caps);
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if (ret < 0)
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@ -197,13 +186,25 @@ static int intel_dp_init_lttpr(struct intel_dp *intel_dp, const u8 dpcd[DP_RECEI
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*/
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int intel_dp_init_lttpr_and_dprx_caps(struct intel_dp *intel_dp)
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{
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u8 dpcd[DP_RECEIVER_CAP_SIZE];
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int lttpr_count;
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struct drm_i915_private *i915 = dp_to_i915(intel_dp);
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int lttpr_count = 0;
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if (drm_dp_read_dpcd_caps(&intel_dp->aux, dpcd))
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return -EIO;
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/*
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* Detecting LTTPRs must be avoided on platforms with an AUX timeout
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* period < 3.2ms. (see DP Standard v2.0, 2.11.2, 3.6.6.1).
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*/
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if (!intel_dp_is_edp(intel_dp) &&
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(DISPLAY_VER(i915) >= 10 && !IS_GEMINILAKE(i915))) {
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u8 dpcd[DP_RECEIVER_CAP_SIZE];
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lttpr_count = intel_dp_init_lttpr(intel_dp, dpcd);
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if (drm_dp_dpcd_probe(&intel_dp->aux, DP_LT_TUNABLE_PHY_REPEATER_FIELD_DATA_STRUCTURE_REV))
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return -EIO;
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if (drm_dp_read_dpcd_caps(&intel_dp->aux, dpcd))
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return -EIO;
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lttpr_count = intel_dp_init_lttpr(intel_dp, dpcd);
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}
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/*
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* The DPTX shall read the DPRX caps after LTTPR detection, so re-read
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