[PATCH RFC 0/4] drm/dp: Rework LTTPR transparent mode handling and add support to msm driver

[Abel Vesa]

Looking at both i915 and nouveau DP drivers, both are setting the first
LTTPR (if found) in transparent mode first and then in non-transparent
mode, just like the DP v2.0 specification mentions in section 3.6.6.1.

Being part of the standard, setting the LTTPR in a specific operation mode
can be easily moved in the generic framework. So do that by adding a new
helper.

Then, the msm DP driver is lacking any kind of support for LTTPR handling,
so add it by reading the LTTPR caps for figuring out the number of LTTPRs
found on plug detect and then do exactly what the i915 and nouveau drivers
do with respect to toggling through operating modes, just like the
up-mentioned section from DP spec describes.

At some point, link training per sub-segment will probably be needed, but
for now, toggling the operating modes seems to be enough at least for the
X Elite-based platforms that this patchset has been tested on.

Signed-off-by: Abel Vesa <abel.vesa at linaro.org>
---
Abel Vesa (4):
      drm/dp: Add helper to set LTTPRs in transparent mode
      drm/nouveau/dp: Use the generic helper to control LTTPR transparent mode
      drm/i915/dp: Use the generic helper to control LTTPR transparent mode
      drm/msm/dp: Add support for LTTPR handling

 drivers/gpu/drm/display/drm_dp_helper.c            | 17 +++++++++++++++
 .../gpu/drm/i915/display/intel_dp_link_training.c  |  2 +-
 drivers/gpu/drm/msm/dp/dp_display.c                | 25 ++++++++++++++++++++++
 drivers/gpu/drm/nouveau/nouveau_dp.c               |  9 +++-----
 include/drm/display/drm_dp_helper.h                |  1 +
 5 files changed, 47 insertions(+), 7 deletions(-)
---
base-commit: 6fb2fa9805c501d9ade047fc511961f3273cdcb5
change-id: 20241031-drm-dp-msm-add-lttpr-transparent-mode-set-136cd5bfde07

Best regards,
-- 
Abel Vesa <abel.vesa at linaro.org>