Re: [PATCH v1 4/6] video/hdmi: Add audio_infoframe packing for DP

[Markus Schneider-Pargmann <msp@baylibre.com>]

Hi Sam,

On Mon, Sep 06, 2021 at 10:30:26PM +0200, Sam Ravnborg wrote:
> Hi Markus,
> 
> On Mon, Sep 06, 2021 at 09:35:27PM +0200, Markus Schneider-Pargmann wrote:
> > Similar to HDMI, DP uses audio infoframes as well which are structured
> > very similar to the HDMI ones.
> > 
> > This patch adds a helper function to pack the HDMI audio infoframe for
> > DP, called hdmi_audio_infoframe_pack_for_dp().
> > hdmi_audio_infoframe_pack_only() is split into two parts. One of them
> > packs the payload only and can be used for HDMI and DP.
> > 
> > Signed-off-by: Markus Schneider-Pargmann <msp@baylibre.com>
> > ---
> >  drivers/video/hdmi.c | 87 +++++++++++++++++++++++++++++++++++---------
> >  include/linux/hdmi.h |  4 ++
> >  2 files changed, 73 insertions(+), 18 deletions(-)
> > 
> > diff --git a/drivers/video/hdmi.c b/drivers/video/hdmi.c
> > index 947be761dfa4..59c4341549e4 100644
> > --- a/drivers/video/hdmi.c
> > +++ b/drivers/video/hdmi.c
> > @@ -387,6 +387,28 @@ int hdmi_audio_infoframe_check(struct hdmi_audio_infoframe *frame)
> >  }
> >  EXPORT_SYMBOL(hdmi_audio_infoframe_check);
> >  
> > +static void
> > +hdmi_audio_infoframe_pack_payload(const struct hdmi_audio_infoframe *frame,
> > +				  u8 *buffer)
> > +{
> > +	u8 channels;
> > +
> > +	if (frame->channels >= 2)
> > +		channels = frame->channels - 1;
> > +	else
> > +		channels = 0;
> > +
> > +	buffer[0] = ((frame->coding_type & 0xf) << 4) | (channels & 0x7);
> > +	buffer[1] = ((frame->sample_frequency & 0x7) << 2) |
> > +		 (frame->sample_size & 0x3);
> > +	buffer[2] = frame->coding_type_ext & 0x1f;
> > +	buffer[3] = frame->channel_allocation;
> > +	buffer[4] = (frame->level_shift_value & 0xf) << 3;
> > +
> > +	if (frame->downmix_inhibit)
> > +		buffer[4] |= BIT(7);
> > +}
> > +
> >  /**
> >   * hdmi_audio_infoframe_pack_only() - write HDMI audio infoframe to binary buffer
> >   * @frame: HDMI audio infoframe
> > @@ -404,7 +426,6 @@ EXPORT_SYMBOL(hdmi_audio_infoframe_check);
> >  ssize_t hdmi_audio_infoframe_pack_only(const struct hdmi_audio_infoframe *frame,
> >  				       void *buffer, size_t size)
> >  {
> > -	unsigned char channels;
> >  	u8 *ptr = buffer;
> >  	size_t length;
> >  	int ret;
> > @@ -420,28 +441,13 @@ ssize_t hdmi_audio_infoframe_pack_only(const struct hdmi_audio_infoframe *frame,
> >  
> >  	memset(buffer, 0, size);
> >  
> > -	if (frame->channels >= 2)
> > -		channels = frame->channels - 1;
> > -	else
> > -		channels = 0;
> > -
> >  	ptr[0] = frame->type;
> >  	ptr[1] = frame->version;
> >  	ptr[2] = frame->length;
> >  	ptr[3] = 0; /* checksum */
> >  
> > -	/* start infoframe payload */
> > -	ptr += HDMI_INFOFRAME_HEADER_SIZE;
> > -
> > -	ptr[0] = ((frame->coding_type & 0xf) << 4) | (channels & 0x7);
> > -	ptr[1] = ((frame->sample_frequency & 0x7) << 2) |
> > -		 (frame->sample_size & 0x3);
> > -	ptr[2] = frame->coding_type_ext & 0x1f;
> > -	ptr[3] = frame->channel_allocation;
> > -	ptr[4] = (frame->level_shift_value & 0xf) << 3;
> > -
> > -	if (frame->downmix_inhibit)
> > -		ptr[4] |= BIT(7);
> > +	hdmi_audio_infoframe_pack_payload(frame,
> > +					  ptr + HDMI_INFOFRAME_HEADER_SIZE);
> >  
> >  	hdmi_infoframe_set_checksum(buffer, length);
> >  
> > @@ -479,6 +485,51 @@ ssize_t hdmi_audio_infoframe_pack(struct hdmi_audio_infoframe *frame,
> >  }
> >  EXPORT_SYMBOL(hdmi_audio_infoframe_pack);
> >  
> > +/**
> > + * hdmi_audio_infoframe_pack_for_dp - Pack a HDMI Audio infoframe for
> > + *                                    displayport
> > + *
> > + * @frame HDMI Audio infoframe
> > + * @header Header buffer to be used
> > + * @header_size Size of header buffer
> > + * @data Data buffer to be used
> > + * @data_size Size of data buffer
> > + * @dp_version Display Port version to be encoded in the header
> > + *
> > + * Packs a HDMI Audio Infoframe to be sent over Display Port. This function
> > + * fills both header and data buffer with the required data.
> > + *
> > + * Return: Number of total written bytes or a negative errno on failure.
> > + */
> > +ssize_t hdmi_audio_infoframe_pack_for_dp(struct hdmi_audio_infoframe *frame,
> > +					 void *header, size_t header_size,
> > +					 void *data, size_t data_size,
> > +					 u8 dp_version)
> > +{
> > +	int ret;
> > +	u8 *hdr_ptr = header;
> > +
> > +	ret = hdmi_audio_infoframe_check(frame);
> > +	if (ret)
> > +		return ret;
> > +
> > +	if (header_size < 4 || data_size < frame->length)
> > +		return -ENOSPC;
> > +
> > +	memset(header, 0, header_size);
> > +	memset(data, 0, data_size);
> > +
> > +	// Secondary-data packet header
> > +	hdr_ptr[1] = frame->type;
> > +	hdr_ptr[2] = 0x1B;  // As documented by DP spec for Secondary-data Packets
> Any constant we could use or define and use here?
> Hard coding 0x1b is the less desireable option.

I couldn't find a constant for this, but I will add one.

Also thanks to looking for these defines, I found a struct dp_sdp that
could be used instead of the header and data pointers which I would
prefer, so I will fix that for the next version.

Thanks for your feedback.

Best,
Markus

> 
> 	Sam
> 
> > +	hdr_ptr[3] = (dp_version & 0x3f) << 2;
> > +
> > +	hdmi_audio_infoframe_pack_payload(frame, data);
> > +
> > +	return frame->length + 4;
> > +}
> > +EXPORT_SYMBOL(hdmi_audio_infoframe_pack_for_dp);
> > +
> >  /**
> >   * hdmi_vendor_infoframe_init() - initialize an HDMI vendor infoframe
> >   * @frame: HDMI vendor infoframe
> > diff --git a/include/linux/hdmi.h b/include/linux/hdmi.h
> > index c8ec982ff498..f576a0b08c85 100644
> > --- a/include/linux/hdmi.h
> > +++ b/include/linux/hdmi.h
> > @@ -334,6 +334,10 @@ struct hdmi_audio_infoframe {
> >  int hdmi_audio_infoframe_init(struct hdmi_audio_infoframe *frame);
> >  ssize_t hdmi_audio_infoframe_pack(struct hdmi_audio_infoframe *frame,
> >  				  void *buffer, size_t size);
> > +ssize_t hdmi_audio_infoframe_pack_for_dp(struct hdmi_audio_infoframe *frame,
> > +					 void *header, size_t header_size,
> > +					 void *data, size_t data_size,
> > +					 u8 dp_version);
> >  ssize_t hdmi_audio_infoframe_pack_only(const struct hdmi_audio_infoframe *frame,
> >  				       void *buffer, size_t size);
> >  int hdmi_audio_infoframe_check(struct hdmi_audio_infoframe *frame);
> > -- 
> > 2.33.0

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