[RFC PATCH 0/2] media: synopsys: hdmirx: add HDMI audio capture support

[Igor Paunovic <royalnet026@gmail.com>]

This series adds audio capture support to the Synopsys DesignWare HDMI
RX driver, which currently handles video only. The controller already
extracts the audio stream embedded in the incoming HDMI signal and can
feed it to an on-SoC I2S interface.

Patch 1 documents #sound-dai-cells in the binding. Patch 2 registers
the generic hdmi-codec as a child device of the controller so that a
simple-audio-card in the device tree can bind the HDMI RX audio DAI.
The audio sample rate is recovered from the ACR N/CTS values together
with the measured TMDS character rate, and a periodic worker keeps the
local audio reference clock locked to the source by nudging it in small
ppm steps to hold the audio FIFO fill level near its target, avoiding
FIFO under/overflow and dropped samples.

Tested on an Orange Pi 5 Plus (RK3588, i2s7_8ch as the capture DAI)
with several HDMI sources: stable capture at 44.1 kHz and 48 kHz,
sample rate switching, long recordings with no drift-related drops, and
live A/V monitoring alongside the existing video capture.

Sent as RFC to ask whether this is the preferred shape for the RX
driver: the hdmi-codec child + DT sound card plumbing follows the
pattern used on the TX side by dw-hdmi. The board-side DT changes
(enabling the I2S interface and adding the sound card) are not part of
this series and would go through the SoC tree separately.

Igor Paunovic (2):
  dt-bindings: media: snps,dw-hdmi-rx: add #sound-dai-cells
  media: synopsys: hdmirx: add HDMI audio capture support

 .../bindings/media/snps,dw-hdmi-rx.yaml       |   7 +
 .../platform/synopsys/hdmirx/snps_hdmirx.c    | 244 ++++++++++++++++++
 .../platform/synopsys/hdmirx/snps_hdmirx.h    |   8 +
 3 files changed, 259 insertions(+)

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2.53.0