Re: [PATCH v5 1/3] drm/bridge: synopsys: Add audio support for dw-hdmi-qp

[Quentin Schulz]

Hi Detlev,

On 2/6/25 9:40 PM, Detlev Casanova wrote:
> Hi Quentin,
>
> On Tuesday, 4 February 2025 04:59:12 EST Quentin Schulz wrote:
> > Hi Detlev,
> >
> > Just some drive-by comment inline.
> >
> > On 2/3/25 6:16 PM, Detlev Casanova wrote:
[...]
> > > +static void dw_hdmi_qp_set_audio_interface(struct dw_hdmi_qp *hdmi,
> > > +					   struct hdmi_codec_daifmt
> *fmt,
> > > +					   struct hdmi_codec_params
> *hparms)
> > > +{
> > > +	u32 conf0 = 0;
> > > +
> > > +	/* Reset the audio data path of the AVP */
> > > +	dw_hdmi_qp_write(hdmi, AVP_DATAPATH_PACKET_AUDIO_SWINIT_P,
> > > GLOBAL_SWRESET_REQUEST); +
> > > +	/* Disable AUDS, ACR, AUDI */
> > > +	dw_hdmi_qp_mod(hdmi, 0,
> > > +		  PKTSCHED_ACR_TX_EN | PKTSCHED_AUDS_TX_EN |
> PKTSCHED_AUDI_TX_EN,
> > > +		  PKTSCHED_PKT_EN);
> > > +
> > > +	/* Clear the audio FIFO */
> > > +	dw_hdmi_qp_write(hdmi, AUDIO_FIFO_CLR_P, AUDIO_INTERFACE_CONTROL0);
> > > +
> > > +	/* Select I2S interface as the audio source */
> > > +	dw_hdmi_qp_mod(hdmi, AUD_IF_I2S, AUD_IF_SEL_MSK,
> > > AUDIO_INTERFACE_CONFIG0); +
> > > +	/* Enable the active i2s lanes */
> > > +	switch (hparms->channels) {
> > > +	case 7 ... 8:
> > > +		conf0 |= I2S_LINES_EN(3);
> > > +		fallthrough;
> > > +	case 5 ... 6:
> > > +		conf0 |= I2S_LINES_EN(2);
> > > +		fallthrough;
> > > +	case 3 ... 4:
> > > +		conf0 |= I2S_LINES_EN(1);
> > > +		fallthrough;
> > > +	default:
> > > +		conf0 |= I2S_LINES_EN(0);
> > > +		break;
> > > +	}
> > > +
> > > +	dw_hdmi_qp_mod(hdmi, conf0, I2S_LINES_EN_MSK,
> AUDIO_INTERFACE_CONFIG0);
> > > +
> > > +	/*
> > > +	 * Enable bpcuv generated internally for L-PCM, or received
> > > +	 * from stream for NLPCM/HBR.
> > > +	 */
> > > +	switch (fmt->bit_fmt) {
> > > +	case SNDRV_PCM_FORMAT_IEC958_SUBFRAME_LE:
> > > +		conf0 = (hparms->channels == 8) ? AUD_HBR : AUD_ASP;
> > > +		conf0 |= I2S_BPCUV_RCV_EN;
> > > +		break;
> > > +	default:
> > > +		conf0 = AUD_ASP | I2S_BPCUV_RCV_DIS;
> > > +		break;
> > > +	}
> > > +
> > > +	dw_hdmi_qp_mod(hdmi, conf0, I2S_BPCUV_RCV_MSK | AUD_FORMAT_MSK,
> > > +		  AUDIO_INTERFACE_CONFIG0);
> > > +
> > > +	/* Enable audio FIFO auto clear when overflow */
> > > +	dw_hdmi_qp_mod(hdmi, AUD_FIFO_INIT_ON_OVF_EN,
> AUD_FIFO_INIT_ON_OVF_MSK,
> > > +		  AUDIO_INTERFACE_CONFIG0);
> >
> > This is all very I2S-centric while the HDMI controllers on RK3588 do
> > have the ability (according to the TRM) to use S/PDIF instead of I2S. I
> > assume the driver should be able to know which format to use based on
> > simple-audio-card,format property? Is that correct? Then current support
> > which doesn't even check for I2S would be fine and not conflict with a
> > later commit which would add support for S/PDIF? (Essentially asking if
> > we need another DT property for the HDMI controller node or elsewhere to
> > specify which mode to run in instead of expecting it to always be I2S).
>
> The hdmi_codec_daifmt::fmt field already has this information, based on the
> simple-audio-card,format = "i2s"; field in the device tree.
>
> I could add a condition in dw_hdmi_qp_audio_prepare() to fail with -EINVAL if
> the devicetree specifies anything else than "i2s" for now.

All I was asking is whether we can (easily) check this property is set 
to i2s the day we want to implement support for S/PDIF :) If that's the 
case, then I don't think we necessarily need to check it right now, but 
a -EINVAL would be fine too, up to you.

> I'm not willing to implement support for the SPDIF path for now, mainly
> because there's no need for that yet (I2S works well) and the downstream
> kernel doesn't implemented it, meaning it hasn't been tested a lot anyway.

That's fine, just wanted to know if a "backward-compatible" 
implementation for S/PDIF would be possible in the future would we want 
to support it :)

Cheers,
Quentin