Tested on latest drm-tip with DPCD=1.2 Sink and LTTPR set to non- transparent mode: [ 706.966375] i915 0000:00:02.0: [drm:drm_dp_dpcd_read] AUX USBC2/DDI TC2/PHY TC2: 0xf0000 AUX -> (ret= 8) 14 1e 80 55 04 00 00 00 [ 706.966383] i915 0000:00:02.0: [drm:intel_dp_init_lttpr_and_dprx_caps [i915]] LTTPR common capabilities: 14 1e 80 55 04 00 00 00 [ 706.966900] i915 0000:00:02.0: [drm:drm_dp_dpcd_write] AUX USBC2/DDI TC2/PHY TC2: 0xf0003 AUX <- (ret= 1) 55 [ 706.967397] i915 0000:00:02.0: [drm:drm_dp_dpcd_write] AUX USBC2/DDI TC2/PHY TC2: 0xf0003 AUX <- (ret= 1) aa [ 706.968384] i915 0000:00:02.0: [drm:drm_dp_dpcd_read] AUX USBC2/DDI TC2/PHY TC2: 0xf0020 AUX -> (ret= 3) 03 00 00 [ 706.968388] i915 0000:00:02.0: [drm:intel_dp_init_lttpr_and_dprx_caps [i915]] LTTPR 1 PHY capabilities: 03 00 00 [ 706.969913] i915 0000:00:02.0: [drm:drm_dp_dpcd_read] AUX USBC2/DDI TC2/PHY TC2: 0x00000 AUX -> (ret= 15) 12 14 c4 01 01 00 01 00 02 02 06 00 00 00 00 [ 706.969917] i915 0000:00:02.0: [drm:drm_dp_read_dpcd_caps] AUX USBC2/DDI TC2/PHY TC2: DPCD: 12 14 c4 01 01 00 01 00 02 02 06 00 00 00 00 Tested-by: Khaled Almahallawy <khaled.almahallawy@xxxxxxxxx> Reviewed-by: Khaled Almahallawy <khaled.almahallawy@xxxxxxxxx> Thank you for the patch ~Khaled On Thu, 2021-05-13 at 00:28 +0300, Imre Deak wrote: > The driver currently disables the LTTPR non-transparent link training > mode for sinks with a DPCD_REV<1.4, based on the following > description > of the LTTPR DPCD register range in DP standard 2.0 (at the 0xF0000 > register description): > > "" > LTTPR-related registers at DPCD Addresses F0000h through F02FFh are > valid > only for DPCD r1.4 (or higher). > """ > > The transparent link training mode should still work fine, however > the > implementation for this in some retimer FWs seems to be broken, see > the > References: link below. > > After discussions with DP standard authors the above "DPCD r1.4" does > not refer to the DPCD revision (stored in the DPCD_REV reg at > 0x00000), > rather to the "LTTPR field data structure revision" stored in the > 0xF0000 reg. An update request has been filed at vesa.org (see > wg/Link/documentComment/3746) for the upcoming v2.1 specification to > clarify the above description along the following lines: > > """ > LTTPR-related registers at DPCD Addresses F0000h through F02FFh are > valid only for LT_TUNABLE_PHY_REPEATER_FIELD_DATA_STRUCTURE_REV 1.4 > (or > higher) > """ > > Based on my tests Windows uses the non-transparent link training mode > for DPCD_REV==1.2 sinks as well (so presumably for all DPCD_REVs), > and > forcing it to use transparent mode on ICL/TGL platforms leads to the > same LT failure as reported at the References: link. > > Based on the above let's assume that the transparent link training > mode > is not well tested/supported and align the code to the correct > interpretation of what the r1.4 version refers to. > > References: https://gitlab.freedesktop.org/drm/intel/-/issues/3415 > Fixes: 264613b406eb ("drm/i915: Disable LTTPR support when the DPCD > rev < 1.4") > Cc: <stable@xxxxxxxxxxxxxxx> # v5.11+ > Signed-off-by: Imre Deak <imre.deak@xxxxxxxxx> > --- > .../drm/i915/display/intel_dp_link_training.c | 71 +++++++++------ > ---- > 1 file changed, 33 insertions(+), 38 deletions(-) > > diff --git a/drivers/gpu/drm/i915/display/intel_dp_link_training.c > b/drivers/gpu/drm/i915/display/intel_dp_link_training.c > index 6bf6f1ec13ed8..08bceae40aa8d 100644 > --- a/drivers/gpu/drm/i915/display/intel_dp_link_training.c > +++ b/drivers/gpu/drm/i915/display/intel_dp_link_training.c > @@ -128,50 +128,14 @@ intel_dp_set_lttpr_transparent_mode(struct > intel_dp *intel_dp, bool enable) > return drm_dp_dpcd_write(&intel_dp->aux, DP_PHY_REPEATER_MODE, > &val, 1) == 1; > } > > -/** > - * intel_dp_init_lttpr_and_dprx_caps - detect LTTPR and DPRX caps, > init the LTTPR link training mode > - * @intel_dp: Intel DP struct > - * > - * Read the LTTPR common and DPRX capabilities and switch to non- > transparent > - * link training mode if any is detected and read the PHY > capabilities for all > - * detected LTTPRs. In case of an LTTPR detection error or if the > number of > - * LTTPRs is more than is supported (8), fall back to the no-LTTPR, > - * transparent mode link training mode. > - * > - * Returns: > - * >0 if LTTPRs were detected and the non-transparent LT mode was > set. The > - * DPRX capabilities are read out. > - * 0 if no LTTPRs or more than 8 LTTPRs were detected or in case > of a > - * detection failure and the transparent LT mode was set. The > DPRX > - * capabilities are read out. > - * <0 Reading out the DPRX capabilities failed. > - */ > -int intel_dp_init_lttpr_and_dprx_caps(struct intel_dp *intel_dp) > +static int intel_dp_init_lttpr(struct intel_dp *intel_dp) > { > int lttpr_count; > - bool ret; > int i; > > - ret = intel_dp_read_lttpr_common_caps(intel_dp); > - > - /* The DPTX shall read the DPRX caps after LTTPR detection. */ > - if (drm_dp_read_dpcd_caps(&intel_dp->aux, intel_dp->dpcd)) { > - intel_dp_reset_lttpr_common_caps(intel_dp); > - return -EIO; > - } > - > - if (!ret) > + if (!intel_dp_read_lttpr_common_caps(intel_dp)) > return 0; > > - /* > - * The 0xF0000-0xF02FF range is only valid if the DPCD revision > is > - * at least 1.4. > - */ > - if (intel_dp->dpcd[DP_DPCD_REV] < 0x14) { > - intel_dp_reset_lttpr_common_caps(intel_dp); > - return 0; > - } > - > lttpr_count = drm_dp_lttpr_count(intel_dp->lttpr_common_caps); > /* > * Prevent setting LTTPR transparent mode explicitly if no > LTTPRs are > @@ -211,6 +175,37 @@ int intel_dp_init_lttpr_and_dprx_caps(struct > intel_dp *intel_dp) > > return lttpr_count; > } > + > +/** > + * intel_dp_init_lttpr_and_dprx_caps - detect LTTPR and DPRX caps, > init the LTTPR link training mode > + * @intel_dp: Intel DP struct > + * > + * Read the LTTPR common and DPRX capabilities and switch to non- > transparent > + * link training mode if any is detected and read the PHY > capabilities for all > + * detected LTTPRs. In case of an LTTPR detection error or if the > number of > + * LTTPRs is more than is supported (8), fall back to the no-LTTPR, > + * transparent mode link training mode. > + * > + * Returns: > + * >0 if LTTPRs were detected and the non-transparent LT mode was > set. The > + * DPRX capabilities are read out. > + * 0 if no LTTPRs or more than 8 LTTPRs were detected or in case > of a > + * detection failure and the transparent LT mode was set. The > DPRX > + * capabilities are read out. > + * <0 Reading out the DPRX capabilities failed. > + */ > +int intel_dp_init_lttpr_and_dprx_caps(struct intel_dp *intel_dp) > +{ > + int lttpr_count = intel_dp_init_lttpr(intel_dp); > + > + /* The DPTX shall read the DPRX caps after LTTPR detection. */ > + if (drm_dp_read_dpcd_caps(&intel_dp->aux, intel_dp->dpcd)) { > + intel_dp_reset_lttpr_common_caps(intel_dp); > + return -EIO; > + } > + > + return lttpr_count; > +} > EXPORT_SYMBOL(intel_dp_init_lttpr_and_dprx_caps); > > static u8 dp_voltage_max(u8 preemph)
