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

[Rex-BC Chen <rex-bc.chen@mediatek.com>]

On Wed, 2022-05-25 at 14:26 +0200, AngeloGioacchino Del Regno wrote:
> 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?
> 

Hello Angelo,

because we do not know whether "HDMI_AUDIO_CODING_TYPE_STREAM" is
compressed, we decide to change this function name to
drm_cea_sad_is_pcm to prevent misunderstanding.
For this, I will drop case HDMI_AUDIO_CODING_TYPE_STREAM

> > +	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;
> }
> 

After sync with Jitao, we think this function is not correct.
refer to table of "Short Audio Descriptor" in [1].

[1]:https://en.wikipedia.org/wiki/Extended_Display_Identification_Data

BRs,
Bo-Chen
> > +/**
> > + * 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);
> >   
> 
> 
> _______________________________________________
> linux-arm-kernel mailing list
> linux-arm-kernel@lists.infradead.org
> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel