My cpu dai driving the tda998x in master mode outputs
SNDRV_PCM_FORMAT_S24_LE, i2s left justified, two channels:
[SNDRV_PCM_FORMAT_S24_LE] = {
.width = 24, .phys = 32, .le = 1, .signd = 1,
.silence = {},
},
This format has a sample width of 24 bits, but a physical
size of 32 bits per channel. The redundant bits are padded
with zeros. This gives a total frame width of 64 bits.
According to the tda19988 datasheet, this format is supported:
"Audio samples with a precision better than 24-bit are
truncated to 24-bit. [...] If the input clock has a
frequency of 64fs and is left justified or Philips,
the audio word is truncated to 24-bit format and other
bits padded with zeros."
(tda19988 product datasheet Rev. 3 - 21 July 2011)
However, supplying this format to the chip results in distorted
audio. I noticed that the audio problem disappears when the
CTS_N pre-divider is calculated from the physical width, _not_
the sample width.
This patch adjusts the CTS_N calculation so that the audio
distortion goes away.
Caveats:
- I am only capable of generating audio with a frame width of
64fs. So I cannot test if 32fs or 48fs audio formats still
work. Such as S16_LE or S20_LE.
- I have no access to a datasheet which accurately describes
the CTS_N register. So I cannot check if my assumption is
correct.
Tested with an imx6 ssi.
Cc: Peter Rosin <p...@axentia.se>
Signed-off-by: Sven Van Asbroeck <thesve...@gmail.com>
---
drivers/gpu/drm/i2c/tda998x_drv.c | 4 ++--
include/drm/i2c/tda998x.h | 2 +-
2 files changed, 3 insertions(+), 3 deletions(-)
diff --git a/drivers/gpu/drm/i2c/tda998x_drv.c
b/drivers/gpu/drm/i2c/tda998x_drv.c
index a7c39f39793f..ba9f55176e1b 100644
--- a/drivers/gpu/drm/i2c/tda998x_drv.c
+++ b/drivers/gpu/drm/i2c/tda998x_drv.c
@@ -893,7 +893,7 @@ tda998x_configure_audio(struct tda998x_priv *priv,
reg_write(priv, REG_MUX_AP, MUX_AP_SELECT_I2S);
clksel_aip = AIP_CLKSEL_AIP_I2S;
clksel_fs = AIP_CLKSEL_FS_ACLK;
- switch (params->sample_width) {
+ switch (params->physical_width) {
case 16:
cts_n = CTS_N_M(3) | CTS_N_K(1);
break;
@@ -982,7 +982,7 @@ static int tda998x_audio_hw_params(struct device *dev, void
*data,
struct tda998x_priv *priv = dev_get_drvdata(dev);
int i, ret;
struct tda998x_audio_params audio = {
- .sample_width = params->sample_width,
+ .physical_width = params->physical_width,
.sample_rate = params->sample_rate,
.cea = params->cea,
};
diff --git a/include/drm/i2c/tda998x.h b/include/drm/i2c/tda998x.h
index 3cb25ccbe5e6..7e9fddcc4ddd 100644
--- a/include/drm/i2c/tda998x.h
+++ b/include/drm/i2c/tda998x.h
@@ -14,7 +14,7 @@ enum {
struct tda998x_audio_params {
u8 config;
u8 format;
- unsigned sample_width;
+ unsigned int physical_width;
unsigned sample_rate;
struct hdmi_audio_infoframe cea;
u8 status[5];
--
2.17.1
