[PATCH v2] drm/bridge: dw-hdmi-i2s: set insert_pcuv bit if hardware supports it

[Geraldo Nascimento]

Starting with version 2.10a of Synopsys DesignWare HDMI controller the
insert_pcuv bit was introduced. On RK3399pro SoM (Radxa Rock Pi N10)
for example if we neglect to set this bit and proceed to enable hdmi_sound
and i2s2 on the device tree there will be extreme clipping of sound
output, to the point that music sounds like white noise. Problem
could also manifest as just mild cracking depending of HDMI audio
implementation of sink. Setting insert_pcuv bit (bit 2 of
aud_conf2 Audio Sample register) fixes this.

Signed-off-by: Geraldo Nascimento <geraldogabriel at gmail.com>

---

v1->v2: SoC->SoM on description, better commenting, minor style changes,
	conditional application of fix for L-PCM only

--- a/drivers/gpu/drm/bridge/synopsys/dw-hdmi-i2s-audio.c
+++ b/drivers/gpu/drm/bridge/synopsys/dw-hdmi-i2s-audio.c
@@ -42,6 +42,7 @@ static int dw_hdmi_i2s_hw_params(struct device *dev, void *data,
 	struct dw_hdmi *hdmi = audio->hdmi;
 	u8 conf0 = 0;
 	u8 conf1 = 0;
+	u8 conf2 = 0;
 	u8 inputclkfs = 0;
 
 	/* it cares I2S only */
@@ -101,6 +102,16 @@ static int dw_hdmi_i2s_hw_params(struct device *dev, void *data,
 		return -EINVAL;
 	}
 
+	/*
+	 * dw-hdmi introduced insert_pcuv bit in
+	 * version 2.10a.
+	 *
+	 * This single bit (bit 2 of HDMI_AUD_CONF2)
+	 * when set to 1 will enable the insertion of the PCUV
+	 * (Parity, Channel Status, User bit and Validity)
+	 * bits on the incoming audio stream.
+	 * 
+	 * Support is limited to Linear PCM audio. If
+	 * neglected, the lack of valid PCUV bits
+	 * on L-PCM streams will cause anything from
+	 * mild cracking to full blown extreme
+	 * clipping depending of HDMI audio
+	 * implementation of the sink.
+	 *
+	 */
+
+	if (hdmi_read(audio, HDMI_DESIGN_ID) >= 0x21 &&
+			!(hparms->iec.status[0] & IEC958_AES0_NONAUDIO))
+		conf2 = HDMI_AUD_CONF2_INSERT_PCUV;
+
 	dw_hdmi_set_sample_rate(hdmi, hparms->sample_rate);
 	dw_hdmi_set_channel_status(hdmi, hparms->iec.status);
 	dw_hdmi_set_channel_count(hdmi, hparms->channels);
@@ -109,6 +120,7 @@ static int dw_hdmi_i2s_hw_params(struct device *dev, void *data,
 	hdmi_write(audio, inputclkfs, HDMI_AUD_INPUTCLKFS);
 	hdmi_write(audio, conf0, HDMI_AUD_CONF0);
 	hdmi_write(audio, conf1, HDMI_AUD_CONF1);
+	hdmi_write(audio, conf2, HDMI_AUD_CONF2);
 
 	return 0;
 }
--- a/drivers/gpu/drm/bridge/synopsys/dw-hdmi.h
+++ b/drivers/gpu/drm/bridge/synopsys/dw-hdmi.h
@@ -931,6 +931,11 @@ enum {
 	HDMI_AUD_CONF1_WIDTH_16 = 0x10,
 	HDMI_AUD_CONF1_WIDTH_24 = 0x18,
 
+/* AUD_CONF2 field values */
+	HDMI_AUD_CONF2_HBR = 0x01,
+	HDMI_AUD_CONF2_NLPCM = 0x02,
+	HDMI_AUD_CONF2_INSERT_PCUV = 0x04,
+
 /* AUD_CTS3 field values */
 	HDMI_AUD_CTS3_N_SHIFT_OFFSET = 5,
 	HDMI_AUD_CTS3_N_SHIFT_MASK = 0xe0,