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

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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@xxxxxxxxxxxx>
Signed-off-by: Guillaume Ranquet <granquet@xxxxxxxxxxxx>
---
  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);




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