[Bug 206575] [amdgpu] [drm] No video signal on resume from suspend, R9 380

[bugzilla-daemon@bugzilla.kernel.org]

https://bugzilla.kernel.org/show_bug.cgi?id=206575

--- Comment #7 from Noel Maersk (veox+kernel@veox.pw) ---
`git bisect log` output at:
https://gist.github.com/veox/36aeb77acfbcaea9c4ba1cc70052329a

Had to `skip` a few because of system instability on v5.5.4 (cause unknown,
likely
unrelated to this bug); switched to v5.4.20 halfway-in to avoid.

Result as follows (e-mails changed).


1ea8751bd28d1ec2b36a56ec6bc1ac28903d09b4 is the first bad commit
commit 1ea8751bd28d1ec2b36a56ec6bc1ac28903d09b4
Author: Noah Abradjian <spam@gmail.com>
Date:   Fri Sep 27 16:30:57 2019 -0400

    drm/amd/display: Make clk mgr the only dto update point

    [Why]

    * Clk Mgr DTO update point did not cover all needed updates, as it included
a
      check for plane_state which does not exist yet when the updater is called
on
      driver startup
    * This resulted in another update path in the pipe programming sequence,
based
      on a dppclk update flag
    * However, this alternate path allowed for stray DTO updates, some of which
would
      occur in the wrong order during dppclk lowering and cause underflow

    [How]

    * Remove plane_state check and use of plane_res.dpp->inst, getting rid
      of sequence dependencies (this results in extra dto programming for
unused
      pipes but that doesn't cause issues and is a small cost)
    * Allow DTOs to be updated even if global clock is equal, to account for
      edge case exposed by diags tests
    * Remove update_dpp_dto call in pipe programming sequence (leave update to
      dppclk_control there, as that update is necessary and shouldn't occur in
clk
      mgr)
    * Remove call to optimize_bandwidth when committing state, as it is not
needed
      and resulted in sporadic underflows even with other fixes in place

    Signed-off-by: Noah Abradjian <spam@gmail.com>
    Reviewed-by: Jun Lei <spam@gmail.com>
    Acked-by: Leo Li <spam@gmail.com>
    Signed-off-by: Alex Deucher <spam@gmail.com>

 .../gpu/drm/amd/display/dc/clk_mgr/dcn20/dcn20_clk_mgr.c   | 14 +++++++++-----
 drivers/gpu/drm/amd/display/dc/clk_mgr/dcn21/rn_clk_mgr.c  |  3 ++-
 drivers/gpu/drm/amd/display/dc/core/dc.c                   |  4 ----
 drivers/gpu/drm/amd/display/dc/dcn20/dcn20_hwseq.c         |  8 +-------
 4 files changed, 12 insertions(+), 17 deletions(-)

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