Re: [PATCH v10 04/21] drm/edid: Add cea_sad helpers for freq/length

[AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>]

Il 23/05/22 12:47, Guillaume Ranquet ha scritto:
> This patch adds two helper functions that extract the frequency and word
> length from a struct cea_sad.
> 
> For these helper functions new defines are added that help translate the
> 'freq' and 'byte2' fields into real numbers.
> 
> Signed-off-by: Markus Schneider-Pargmann <msp@baylibre.com>
> Signed-off-by: Guillaume Ranquet <granquet@baylibre.com>
> ---
>   drivers/gpu/drm/drm_edid.c | 74 ++++++++++++++++++++++++++++++++++++++
>   include/drm/drm_edid.h     | 14 ++++++++
>   2 files changed, 88 insertions(+)
> 
> diff --git a/drivers/gpu/drm/drm_edid.c b/drivers/gpu/drm/drm_edid.c
> index 561f53831e29..61ef1b1c972c 100644
> --- a/drivers/gpu/drm/drm_edid.c
> +++ b/drivers/gpu/drm/drm_edid.c
> @@ -4758,6 +4758,80 @@ int drm_edid_to_speaker_allocation(struct edid *edid, u8 **sadb)
>   }
>   EXPORT_SYMBOL(drm_edid_to_speaker_allocation);
>   
> +/**
> + * drm_cea_sad_get_sample_rate - Extract the sample rate from cea_sad
> + * @sad: Pointer to the cea_sad struct
> + *
> + * Extracts the cea_sad frequency field and returns the sample rate in Hz.
> + *
> + * Return: Sample rate in Hz or a negative errno if parsing failed.
> + */
> +int drm_cea_sad_get_sample_rate(const struct cea_sad *sad)
> +{
> +	switch (sad->freq) {
> +	case DRM_CEA_SAD_FREQ_32KHZ:
> +		return 32000;
> +	case DRM_CEA_SAD_FREQ_44KHZ:
> +		return 44100;
> +	case DRM_CEA_SAD_FREQ_48KHZ:
> +		return 48000;
> +	case DRM_CEA_SAD_FREQ_88KHZ:
> +		return 88200;
> +	case DRM_CEA_SAD_FREQ_96KHZ:
> +		return 96000;
> +	case DRM_CEA_SAD_FREQ_176KHZ:
> +		return 176400;
> +	case DRM_CEA_SAD_FREQ_192KHZ:
> +		return 192000;
> +	default:
> +		return -EINVAL;
> +	}
> +}
> +EXPORT_SYMBOL(drm_cea_sad_get_sample_rate);
> +
> +static bool drm_cea_sad_is_uncompressed(const struct cea_sad *sad)
> +{
> +	switch (sad->format) {
> +	case HDMI_AUDIO_CODING_TYPE_STREAM:

As far as I know, bit 0 is reserved, so HDMI_AUDIO_CODING_TYPE_STREAM should
never occur here?

> +	case HDMI_AUDIO_CODING_TYPE_PCM:
> +		return true;
> +	default:
> +		return false;
> +	}
> +}
> +

Also, I think that implementing a drm_cea_sad_get_compressed_max_bitrate()
function should be pretty straightforward... the spec says that this is
8 bits, byte 3 (your byte2) contains the max bitrate divided by 8kHz,
so to extract it, you read byte2 and multiply it by 8000Hz.

/**
  * drm_cea_sad_get_compressed_max_bitrate - Extract maximum bitrate
  * @sad: Pointer to the cea_sad structure
  *
  * Extracts the cea_sad byte2 field and returns the maximum bit rate
  * of a compressed audio stream.
  *
  * Note: This function may only be called for compressed audio.
  *
  * Return: Maximum bitrate of compressed audio stream in bit/s or
  *         negative number for error
  */
int drm_cea_sad_get_compressed_max_bitrate(const struct cea_sad *sad)
{
	if (drm_cea_sad_is_uncompressed(sad)) {
		DRM_ERROR("Not supported: tried to get max bitrate for uncompressed format: %u\n",
			 sad->format);
		return -EINVAL;
	}

	return sad->byte2 * 8000;
}

> +/**
> + * drm_cea_sad_get_uncompressed_word_length - Extract word length
> + * @sad: Pointer to the cea_sad struct
> + *
> + * Extracts the cea_sad byte2 field and returns the word length for an
> + * uncompressed stream.
> + *
> + * Note: This function may only be called for uncompressed audio.
> + *
> + * Return: Word length in bits or a negative errno if parsing failed.
> + */
> +int drm_cea_sad_get_uncompressed_word_length(const struct cea_sad *sad)
> +{
> +	if (!drm_cea_sad_is_uncompressed(sad)) {
> +		DRM_WARN("Unable to get the uncompressed word length for a compressed format: %u\n",
> +			 sad->format);
> +		return -EINVAL;
> +	}
> +
> +	switch (sad->byte2) {
> +	case DRM_CEA_SAD_UNCOMPRESSED_WORD_16BIT:
> +		return 16;
> +	case DRM_CEA_SAD_UNCOMPRESSED_WORD_20BIT:
> +		return 20;
> +	case DRM_CEA_SAD_UNCOMPRESSED_WORD_24BIT:
> +		return 24;
> +	default:
> +		return -EINVAL;
> +	}
> +}
> +EXPORT_SYMBOL(drm_cea_sad_get_uncompressed_word_length);
> +
>   /**
>    * drm_av_sync_delay - compute the HDMI/DP sink audio-video sync delay
>    * @connector: connector associated with the HDMI/DP sink
> diff --git a/include/drm/drm_edid.h b/include/drm/drm_edid.h
> index 37c420423625..7a939cb95b38 100644
> --- a/include/drm/drm_edid.h
> +++ b/include/drm/drm_edid.h
> @@ -373,6 +373,18 @@ struct cea_sad {
>   	u8 byte2;
>   };
>   
> +#define DRM_CEA_SAD_FREQ_32KHZ  BIT(0)
> +#define DRM_CEA_SAD_FREQ_44KHZ  BIT(1)
> +#define DRM_CEA_SAD_FREQ_48KHZ  BIT(2)
> +#define DRM_CEA_SAD_FREQ_88KHZ  BIT(3)
> +#define DRM_CEA_SAD_FREQ_96KHZ  BIT(4)
> +#define DRM_CEA_SAD_FREQ_176KHZ BIT(5)
> +#define DRM_CEA_SAD_FREQ_192KHZ BIT(6)
> +
> +#define DRM_CEA_SAD_UNCOMPRESSED_WORD_16BIT BIT(0)
> +#define DRM_CEA_SAD_UNCOMPRESSED_WORD_20BIT BIT(1)
> +#define DRM_CEA_SAD_UNCOMPRESSED_WORD_24BIT BIT(2)
> +
>   struct drm_encoder;
>   struct drm_connector;
>   struct drm_connector_state;
> @@ -380,6 +392,8 @@ struct drm_display_mode;
>   
>   int drm_edid_to_sad(struct edid *edid, struct cea_sad **sads);
>   int drm_edid_to_speaker_allocation(struct edid *edid, u8 **sadb);
> +int drm_cea_sad_get_sample_rate(const struct cea_sad *sad);
> +int drm_cea_sad_get_uncompressed_word_length(const struct cea_sad *sad);
>   int drm_av_sync_delay(struct drm_connector *connector,
>   		      const struct drm_display_mode *mode);
>