[v4,0/4] drm/dp: Rework LTTPR transparent mode handling and add support to msm driver

Message

Abel Vesa Jan. 8, 2025, 2:31 p.m. UTC

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 <[e-mail]>
---
Changes in v4:
- Picked up Dmitry's and Johan's R-b tags for the drm generic and drm
  msm patches.
- Moved the comment about the roll-back to transparent mode inside the
  if statement and fixed the typos, like Johan suggested.
- Added more details in the commit message for the i915 changes. Details
  about the update that the lttpr_common_caps need w.r.t. rollback to
  transparent mode in case of failure.
- Link to v3: https://lore.kernel.org/r/2025[e-mail]

Changes in v3:
- Picked-up T-b tag from Johan for the drm/dp transparent mode set helper
  patch
- Re-worked the return value of the drm/dp transparet mode set helper
- Added some more details about what the values of the lttpr_count arg
  is expected to be for the drm_dp_lttpr_init(), like Johan suggested.
- Re-worked the non-transparent mode disable->enable so that the rollback
  doesn't happen unless enable failed.
- Picked-up Lyude's R-b tag for the nouveau patch.
- Dropped extra parantesis at the end of the drm_dp_lttpr_init() call in
  i915 patch.
- Picked-up Johan's T-b tag for the drm/msm/dp patch.
- Added some error handling and an error message in the
  msm_dp_display_lttpr_init(), while dropping the unnecessary lttpr_count
  local variable.
- Link to v2: https://lore.kernel.org/r/2024[e-mail]

Changes in v2:
- Added new wrapper over the set_transparent new helper in order to
  move the non-transparent disable and the its enable->disable sequence
  mentioned in the DP standard section 3.6.6.1 entirely in the generic
  implemetation.
- Switch all 3 drivers to use the new wrapper.
- Fixed the return value of the helper to return 0 on success and
  negative value on error.
- Added explanation about the transparent/non-transparent modes into the
  msm dp commit message.
- Dropped the condition for non-eDP in msm DP driver since it is allowed
  to try to get the number of LTTPRs even on eDP and it will be always
  0 anyway.
- Dropped the RFC prefix
- Link to v1: https://lore.kernel.org/r/2024[e-mail]

---
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            | 62 ++++++++++++++++++++++
 .../gpu/drm/i915/display/intel_dp_link_training.c  | 24 ++-------
 drivers/gpu/drm/msm/dp/dp_display.c                | 17 ++++++
 drivers/gpu/drm/nouveau/nouveau_dp.c               | 17 +-----
 include/drm/display/drm_dp_helper.h                |  2 +
 5 files changed, 88 insertions(+), 34 deletions(-)
---
base-commit: 7b4b9bf203da94fbeac75ed3116c84aa03e74578
change-id: 20241031-drm-dp-msm-add-lttpr-transparent-mode-set-136cd5bfde07

Best regards,