linux-kernel - RE: [PATCH v10 03/10] drm/connector: implement generic HDMI audio helpers

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Message-ID: <20241231004311.2574720-1-martin.blumenstingl@googlemail.com>
Date: Tue, 31 Dec 2024 01:43:11 +0100
From: Martin Blumenstingl <martin.blumenstingl@...glemail.com>
To: dmitry.baryshkov@...aro.org
Cc: Laurent.pinchart@...asonboard.com,
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Subject: RE: [PATCH v10 03/10] drm/connector: implement generic HDMI audio helpers

Hello Dmitry,

this is great work - thanks for your efforts!

To give some context:
I am working on a HDMI controller driver for the Amlogic Meson8/8b/8m2
SoCs. Unfortunately the driver is not mature enough for upstream
submission (all I have is the vendor driver which serves as reference).
That said, my goal is to upstream the driver at some point. I have
already switched my driver to use hdmi_{clear,write}_infoframe. Now
I'm trying this series to simplify my code even further - by using
your audio helper work!

> --- /dev/null
> +++ b/drivers/gpu/drm/display/drm_hdmi_audio_helper.c
> @@ -0,0 +1,190 @@
> [...]
> +static const struct hdmi_codec_ops drm_connector_hdmi_audio_ops = {
> +	.audio_startup = drm_connector_hdmi_audio_startup,
> +	.prepare = drm_connector_hdmi_audio_prepare,
> +	.audio_shutdown = drm_connector_hdmi_audio_shutdown,
> +	.mute_stream = drm_connector_hdmi_audio_mute_stream,
> +	.get_eld = drm_connector_hdmi_audio_get_eld,
> +	.get_dai_id = drm_connector_hdmi_audio_get_dai_id,
> +	.hook_plugged_cb = drm_connector_hdmi_audio_hook_plugged_cb,
> +};
On my platform drm_connector_hdmi_audio_prepare() is never called. As
a result of that the audio infoframe is never written to my HDMI
controller hardware (hdmi_write_infoframe() is never called with type
HDMI_INFOFRAME_TYPE_AUDIO). My hack to make it work is to add the
following line to drm_connector_hdmi_audio_ops:
  .hw_params = drm_connector_hdmi_audio_prepare,

I checked all instances of struct hdmi_codec_ops in v6.13-rc3 and it
seems that there is only a single driver which uses the .prepare
callback (drivers/gpu/drm/vc4/vc4_hdmi.c). All other drivers seem to
implement .hw_params instead.

The audio controller code for my platform is already upstream:
- sound/soc/meson/aiu-codec-ctrl.c
- sound/soc/meson/aiu-encoder-i2s.c
- sound/soc/meson/aiu-fifo-i2s.c

My understanding is that you have a platform with a lontium-lt9611
HDMI controller available for testing. Can you please help me
investigate and find out which piece of code is calling
hdmi_codec_prepare() and therefore lt9611_hdmi_audio_prepare() on
your board?


Thank you and best regards,
Martin