[Intel-gfx] [RFC 3/3] drm/i915/display: Add wrapper to Compute SAD

[Mitul Golani <mitulkumar.ajitkumar.golani@intel.com>]

Compute SADs that takes into account the supported rate
and channel based on the capabilities of the audio source.
This wrapper function should encapsulate the logic for
determining the supported rate and channel and should
return a set of SADs that are compatible with the source.

--v1:
- call intel_audio_compute_eld in this commit as it is
defined here

--v2:
- Handle case when max frequency is less than 32k.
- remove drm prefix.
- name change for parse_sad to eld_to_sad.

--v3:
- Use signed int wherever required.
- add debug trace when channel is limited.

--v4:
- remove inline from eld_to_sad.
- declare index outside of for loop with int type.
- Correct mask value calculation.
- remove drm_err, instead just return if eld parsing failed.
- remove unncessary typecast
- reduce indentation while parsing sad
- use intel_audio_compute_eld as static and call bandwidth
calculation just before that.

Signed-off-by: Mitul Golani <mitulkumar.ajitkumar.golani@intel.com>
---
 drivers/gpu/drm/i915/display/intel_audio.c | 73 +++++++++++++++++++++-
 1 file changed, 72 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/display/intel_audio.c b/drivers/gpu/drm/i915/display/intel_audio.c
index 79377e33a59b..9f4fc3f9b224 100644
--- a/drivers/gpu/drm/i915/display/intel_audio.c
+++ b/drivers/gpu/drm/i915/display/intel_audio.c
@@ -806,6 +806,77 @@ static void calc_audio_config_params(struct intel_crtc_state *pipe_config)
 	pipe_config->audio.max_channel_count = 0;
 }
 
+static int sad_to_channels(const u8 *sad)
+{
+	return 1 + (sad[0] & 0x7);
+}
+
+static u8 *eld_to_sad(u8 *eld)
+{
+	int ver, mnl;
+
+	ver = (eld[DRM_ELD_VER] & DRM_ELD_VER_MASK) >> DRM_ELD_VER_SHIFT;
+	if (ver != 2 && ver != 31)
+		return NULL;
+
+	mnl = drm_eld_mnl(eld);
+	if (mnl > 16)
+		return NULL;
+
+	return eld + DRM_ELD_CEA_SAD(mnl, 0);
+}
+
+static int get_supported_freq_mask(struct intel_crtc_state *crtc_state)
+{
+	int rate[] = { 32000, 44100, 48000, 88000, 96000, 176000, 192000 };
+	int mask = 0, index;
+
+	for (index = 0; index < ARRAY_SIZE(rate); index++) {
+		if (rate[index] > crtc_state->audio.max_rate)
+			break;
+
+		mask |= 1 << index;
+
+		if (crtc_state->audio.max_rate != rate[index])
+			continue;
+	}
+
+	return mask;
+}
+
+static void intel_audio_compute_eld(struct intel_crtc_state *crtc_state)
+{
+	struct drm_i915_private *i915 = to_i915(crtc_state->uapi.crtc->dev);
+	u8 *eld, *sad;
+	int index, mask = 0;
+
+	eld = crtc_state->eld;
+	if (!eld)
+		return;
+
+	sad = eld_to_sad(eld);
+	if (!sad)
+		return;
+
+	calc_audio_config_params(crtc_state);
+
+	mask = get_supported_freq_mask(crtc_state);
+	for (index = 0; index < drm_eld_sad_count(eld); index++, sad += 3) {
+		/*
+		 * Respect source restricitions. Limit capabilities to a subset that is
+		 * supported both by the source and the sink.
+		 */
+		if (sad_to_channels(sad) >= crtc_state->audio.max_channel_count) {
+			sad[0] &= ~0x7;
+			sad[0] |= crtc_state->audio.max_channel_count - 1;
+			drm_dbg_kms(&i915->drm, "Channel count is limited to %d\n",
+				    crtc_state->audio.max_channel_count - 1);
+		}
+
+		sad[1] &= mask;
+	}
+}
+
 bool intel_audio_compute_config(struct intel_encoder *encoder,
 				struct intel_crtc_state *crtc_state,
 				struct drm_connector_state *conn_state)
@@ -827,7 +898,7 @@ bool intel_audio_compute_config(struct intel_encoder *encoder,
 
 	crtc_state->eld[6] = drm_av_sync_delay(connector, adjusted_mode) / 2;
 
-	calc_audio_config_params(crtc_state);
+	intel_audio_compute_eld(crtc_state);
 
 	return true;
 }
-- 
2.25.1