drm/i915/display: Enable periodic AS SDP skip frames

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When Panel Replay is active the transcoder timing generator runs at the
panel's maximum refresh rate. To drive the panel down to its minimum
refresh rate the Adaptive-Sync SDP (AS SDP) only needs to reach the panel
once per minimum-rate frame, so transmitting it on every (maximum-rate)
frame is redundant and shows up as repeated SDPs on the link.

Xe3p_LPD adds a HW skip-frame counter in PR_ALPM_CTL that lets the source
send a single AS SDP and then suppress it for a programmed number of
frames. Program this counter so that one AS SDP is followed by
(max_vrefresh / min_vrefresh - 1) idle frames, i.e. one AS SDP per
slowest panel frame, allowing the link to be driven down to as low as
1Hz when the hardware supports it.

The maximum and minimum refresh rates come from the panel's adaptive-sync
monitor range, so the skip count is a function of the sink's capabilities
and independent of the current content/flip rate. If the panel does not
advertise a usable range the skip counter is left at zero, i.e. the
feature is a no-op and AS SDP continues to be sent on every frame.

Periodic AS SDP drives the panel down to its minimum refresh rate on its
own, so it is only programmed when VRR is not actively driving the
refresh rate.

The skip-frame mechanism relies on the AS SDP still being transmitted
(just less often) while Panel Replay is active, so when a non-zero
skip-frame count is programmed both
PR_ALPM_CTL_AS_SDP_TRANSMISSION_IN_ACTIVE_DISABLE and
PR_ALPM_CTL_USE_DC3CO_IDLE_PROTOCOL are left cleared. The previous
behaviour (honouring disable_as_sdp_when_pr_active and the DC3CO idle
protocol) is retained for the non skip-frame case.

v3: Fixed Sashiko review findings

v2: Decoupled CMMRR dependency and using sink refresh rate range for
skip frame claculations. This addresses Dibin's review feedback as well.

Assisted-by: Claude:claude-opus-4-8
Signed-off-by: Uma Shankar <uma.shankar@intel.com>
Reviewed-by: Dibin Moolakadan Subrahmanian <dibin.moolakadan.subrahmanian@intel.com>
Tested-by: Naladala Ramanaidu <ramanaidu.naladala@intel.com>
Link: https://patch.msgid.link/20260909080810.2202879-2-uma.shankar@intel.com

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This commit is contained in:

Uma Shankar 2026-09-09 13:38:07 +05:30

parent 9977e9d84f

commit 8dbe5c47ca

2 changed files with 58 additions and 5 deletions

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61

drivers/gpu/drm/i915/display/intel_alpm.c

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2

drivers/gpu/drm/i915/display/intel_psr_regs.h

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