| Message ID | 20250203-drm-dp-msm-add-lttpr-transparent-mode-set-v5-4-c865d0e56d6e@linaro.org (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | drm/dp: Rework LTTPR transparent mode handling and add support to msm driver | expand |
On 2/3/2025 2:57 AM, Abel Vesa wrote: > Link Training Tunable PHY Repeaters (LTTPRs) are defined in DisplayPort > 1.4a specification. As the name suggests, these PHY repeaters are > capable of adjusting their output for link training purposes. > > According to the DisplayPort standard, LTTPRs have two operating > modes: > - non-transparent - it replies to DPCD LTTPR field specific AUX > requests, while passes through all other AUX requests > - transparent - it passes through all AUX requests. > > Switching between these two modes is done by the DPTX by issuing > an AUX write to the DPCD PHY_REPEATER_MODE register. > > The msm DP driver is currently lacking any handling of LTTPRs. > This means that if at least one LTTPR is found between DPTX and DPRX, > the link training would fail if that LTTPR was not already configured > in transparent mode. > > The section 3.6.6.1 from the DisplayPort v2.0 specification mandates > that before link training with the LTTPR is started, the DPTX may place > the LTTPR in non-transparent mode by first switching to transparent mode > and then to non-transparent mode. This operation seems to be needed only > on first link training and doesn't need to be done again until device is > unplugged. > > It has been observed on a few X Elite-based platforms which have > such LTTPRs in their board design that the DPTX needs to follow the > procedure described above in order for the link training to be successful. > > So add support for reading the LTTPR DPCD caps to figure out the number > of such LTTPRs first. Then, for platforms (or Type-C dongles) that have > at least one such an LTTPR, set its operation mode to transparent mode > first and then to non-transparent, just like the mentioned section of > the specification mandates. > > Tested-by: Johan Hovold <johan+linaro@kernel.org> > Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org> > Reviewed-by: Johan Hovold <johan+linaro@kernel.org> > Signed-off-by: Abel Vesa <abel.vesa@linaro.org> > --- > drivers/gpu/drm/msm/dp/dp_display.c | 15 +++++++++++++++ > 1 file changed, 15 insertions(+) > Reviewed-by: Abhinav Kumar <quic_abhinavk@quicinc.com>
diff --git a/drivers/gpu/drm/msm/dp/dp_display.c b/drivers/gpu/drm/msm/dp/dp_display.c index 24dd37f1682bf5016bb0efbeb44489061deff060..1dd8f94e27475ae5b5b25d80f758968e6818f6cc 100644 --- a/drivers/gpu/drm/msm/dp/dp_display.c +++ b/drivers/gpu/drm/msm/dp/dp_display.c @@ -367,6 +367,19 @@ static int msm_dp_display_send_hpd_notification(struct msm_dp_display_private *d return 0; } +static void msm_dp_display_lttpr_init(struct msm_dp_display_private *dp) +{ + u8 lttpr_caps[DP_LTTPR_COMMON_CAP_SIZE]; + int rc; + + if (drm_dp_read_lttpr_common_caps(dp->aux, dp->panel->dpcd, lttpr_caps)) + return; + + rc = drm_dp_lttpr_init(dp->aux, drm_dp_lttpr_count(lttpr_caps)); + if (rc) + DRM_ERROR("failed to set LTTPRs transparency mode, rc=%d\n", rc); +} + static int msm_dp_display_process_hpd_high(struct msm_dp_display_private *dp) { struct drm_connector *connector = dp->msm_dp_display.connector; @@ -377,6 +390,8 @@ static int msm_dp_display_process_hpd_high(struct msm_dp_display_private *dp) if (rc) goto end; + msm_dp_display_lttpr_init(dp); + msm_dp_link_process_request(dp->link); if (!dp->msm_dp_display.is_edp)