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

[Sam Ravnborg <sam@ravnborg.org>]

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.

	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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