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drm/amd/display: Register DCN as a PMFW DF C-state client on DCN42

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[Why]
DCN must not gate DF C-state locally via the DCHUBBUB ALLOW_SELF_REFRESH
controls: forcing a local "disallow" during MM-stutter re-entry can wedge the
fabric and hang boot. When DCN is disallowing c-state or has invalid watermarks
we should be explicit about it rather than using the watermark force selector.

[How]
Register DCN as a client of PMFW's DF C-state arbiter and signal over DALSMC
whether DCN permits DF C-state; PMFW allows DF C-state only once every client
(including DCN) has voted "allow".

- dc_clocks.cstate_allow: last DCN vote acked by PMFW
- clk_mgr_funcs::notify_cstate_disable(clk_mgr, disable)

prepare_bandwidth and headless dc_power_down_on_boot vote Allow;
hardware_release votes Disallow; init_clocks
(D0 entry) only clears the cache (cstate_allow) so the next allow re-syncs with
PMFW.

Reviewed-by: Nicholas Kazlauskas <nicholas.kazlauskas@amd.com>
Signed-off-by: Leo Chen <leo.chen@amd.com>
Signed-off-by: Wayne Lin <wayne.lin@amd.com>
Tested-by: Dan Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
This commit is contained in:
Leo Chen 2026-07-09 14:47:38 -04:00 • committed by Alex Deucher
commit 53845307d5
8 changed files with 91 additions and 1 deletions
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