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drm/display: scdc-helper: Add helper to set SCDC version information

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The HDMI 2.x specs mandate that compliant Sink devices report their SCDC
version in the Sink Version register, which reads as 1 on any
SCDC-capable sink.

There is also a dedicated Source Version register.  Writing it is not
compulsory, but the spec advises that compliant Source devices do so, in
which case the value must be 1.

Add drm_scdc_set_source_version() to follow this recommendation.  The
Sink Version register is read first, both to log the advertised SCDC
version and to guard against non-conformant devices: a sink reporting
version 0 is either not SCDC-version-aware or broken, so writing the
source version gains nothing and risks upsetting such hardware.  In that
case the write is skipped.

The source version is passed as a parameter rather than hardcoded, as
future spec revisions may define additional rules for the allowable
version values.  The written value is additionally clamped to the sink's
reported version so the source never advertises a version the sink does
not understand.

Acked-by: Maxime Ripard <mripard@kernel.org>
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com>
Tested-by: Maud Spierings <maud_spierings@hotmail.com>
Tested-by: Diederik de Haas <diederik@cknow-tech.com>  # NanoPC-T6 LTS, Rock 5B
Tested-by: Igor Paunovic <royalnet026@gmail.com> # RK3588 Orange Pi 5 Plus, dual HDMI
Tested-by: Robin Räber <robin.raebi@gmail.com>
Link: https://patch.msgid.link/20260901-dw-hdmi-qp-scramb-v11-9-bc12954a0688@collabora.com
Signed-off-by: Cristian Ciocaltea <cristian.ciocaltea@collabora.com>
This commit is contained in:
Cristian Ciocaltea 2026-09-01 21:50:33 +03:00
commit f57c219838
2 changed files with 49 additions and 3 deletions
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