[Letux-kernel] Letux/Alpha 400: small progress with sound

[H. Nikolaus Schaller]

Hi Paul,


> Am 27.04.2021 um 13:12 schrieb H. Nikolaus Schaller <hns at goldelico.com>:
> 
> Hi Paul,
> I have managed to get the headset detection work with lewtux-5.12 by modifying the DTS [1]:
> 
> Still no success with I2S/Codec/DMA/aplay/arecord:
> 
> root at letux:~# aplay /usr/share/sounds/alsa/Front_Center.wav
> [ 7637.981286] jz4740_i2s_startup
> [ 7637.984612] ak4642_dai_startup: play=1
> Playing WAVE '/usr/share/sounds/alsa/Front_Center.wav' : Signed 16 bit Little Endian, Rate 48000 Hz, Mono
> [ 7638.024581] ak4642_dai_hw_params mcko=12000000
> [ 7638.029615] ak4642_set_mcko: freq=12000000
> [ 7638.033961] jz4740_i2s_hw_params
> [ 7638.039801] jz4780_dma_config
> [ 7638.054218] jz4780_dma_prep_dma_cyclic
> [ 7638.058211] jz4780_dma_desc_alloc
> [ 7638.061724] jz4780_dma_setup_hwdesc
> [ 7638.065403] jz4780_dma_transfer_size
> [ 7638.069167] jz4780_dma_setup_hwdesc
> [ 7638.072841] jz4780_dma_transfer_size
> [ 7638.076603] jz4780_dma_setup_hwdesc
> [ 7638.080277] jz4780_dma_transfer_size
> [ 7638.084038] jz4780_dma_setup_hwdesc
> [ 7638.087713] jz4780_dma_transfer_size
> [ 7638.091482] jz4780_dma_begin
> [ 7638.094547] jz4780_dma_chan_enable
> [ 7638.098145] jz4740_i2s_trigger
> [ 7638.106437] jz4780_dma_tx_status
> ^CAborted by signal Interrupt...
> [ 7641.548540] jz4740_i2s_trigger
> [ 7641.553011] jz4780_dma_terminate_all
> [ 7641.556778] jz4780_dma_chan_disable
> [ 7641.560456] jz4780_dma_desc_free
> aplay: pcm_write:1939: write error: Inte[ 7641.567445] jz4740_i2s_shutdown
> rrupted system c[ 7641.571680] ak4642_dai_shutdown: play=1
> all
> [ 7641.577012] jz4780_dma_synchronize
> [ 7641.583599] jz4780_dma_chan_disable
> root at letux:~#
> 
> Most likely the clocks of the I2S interface are not enabled properly or the pinctrl
> function / direction is wrong. The fact that aplay gets stuck indicates that the
> jz4730 I2S is in slave mode (waiting for external clock) which is not provided by
> the codec (master). If it were the other way round, sound data would be emitted
> independently of the codec listening or not.

I have hacked some ioremap() into jz4740_i2s_trigger() to be able to modify
pinctrl on the fly and read the gpio bits directly.

There is clock activity on both BITCLK and SYNC obviously coming from the codec.
And switching to ping function 0x2 makes these pins an output.

So I think we can rule out codec and pinctrl problems as the main blocking point
for completely stuck communication. It still may happen that there is no sound
if we fix that but aplay Front_Center.wav should finish playing after ca. 3 seconds.

There remains only the AC97/I2S driver as the location of the issue.

I have now checked the register model of jz4730 and jz4740 and there is a handful
of extra bits for the jz4740. Mainly it is possible to control input and output
channel which separately and jz4740 can do fancy things linke swapping byte order
or outputting stereo for mono etc.

Maybe the driver is setting some register under the wrong assumption that it is
a jz4740.

Next, I'll try to dump the AC97 registers in jz4740_i2s_trigger() where everything
should have been set up properly...

Modifying code isn't difficult. We already have a DT compatible for jz4730-i2s and
a ->version field in the device struct. Small differences are already handled
for jz4760 and jz4770 by this mechanism.

BR,
Nikolaus