[PATCH] ASoC: bcm2835-i2s: substream alignment now independent in hwparams

[Matt Flax]

On 27/3/20 10:56 am, Matt Flax wrote:
>
> Should this patch be handled through the ALSA team the R. Pi team or 
> the BCM team ?
>

Resending again with reduced recipients.


>
> thanks
>
> Matt
>
> On 24/3/20 8:08 pm, Matt Flax wrote:
>> Substream sample alignment was being set in hwparams for both
>> substreams at the same time. This became a problem when    the Audio
>> Injector isolated sound card needed to offset sample alignment
>> for high sample    rates. The latency difference between playback
>> and capture occurs because of the digital isolation chip
>> propagation time, particularly when the codec is master and
>> the DAC return is twice delayed.
>>
>> This patch sets sample alignment registers  based on the substream
>> direction in hwparams. This gives the machine driver more control
>> over sample alignment in the bcm2835 i2s driver.
>>
>> Signed-off-by: Matt Flax <flatmax at flatmax.org>
>> ---
>>   sound/soc/bcm/bcm2835-i2s.c | 36 +++++++++++++++++++-----------------
>>   1 file changed, 19 insertions(+), 17 deletions(-)
>>
>> diff --git a/sound/soc/bcm/bcm2835-i2s.c b/sound/soc/bcm/bcm2835-i2s.c
>> index e6a12e271b07..9db542699a13 100644
>> --- a/sound/soc/bcm/bcm2835-i2s.c
>> +++ b/sound/soc/bcm/bcm2835-i2s.c
>> @@ -493,11 +493,6 @@ static int bcm2835_i2s_hw_params(struct 
>> snd_pcm_substream *substream,
>>           return -EINVAL;
>>       }
>>   -    bcm2835_i2s_calc_channel_pos(&rx_ch1_pos, &rx_ch2_pos,
>> -        rx_mask, slot_width, data_delay, odd_slot_offset);
>> -    bcm2835_i2s_calc_channel_pos(&tx_ch1_pos, &tx_ch2_pos,
>> -        tx_mask, slot_width, data_delay, odd_slot_offset);
>> -
>>       /*
>>        * Transmitting data immediately after frame start, eg
>>        * in left-justified or DSP mode A, only works stable
>> @@ -508,19 +503,26 @@ static int bcm2835_i2s_hw_params(struct 
>> snd_pcm_substream *substream,
>>               "Unstable slave config detected, L/R may be swapped");
>>         /*
>> -     * Set format for both streams.
>> -     * We cannot set another frame length
>> -     * (and therefore word length) anyway,
>> -     * so the format will be the same.
>> +     * Set format on a per stream basis.
>> +     * The alignment format can be different depending on direction.
>>        */
>> -    regmap_write(dev->i2s_regmap, BCM2835_I2S_RXC_A_REG,
>> -          format
>> -        | BCM2835_I2S_CH1_POS(rx_ch1_pos)
>> -        | BCM2835_I2S_CH2_POS(rx_ch2_pos));
>> -    regmap_write(dev->i2s_regmap, BCM2835_I2S_TXC_A_REG,
>> -          format
>> -        | BCM2835_I2S_CH1_POS(tx_ch1_pos)
>> -        | BCM2835_I2S_CH2_POS(tx_ch2_pos));
>> +    if (substream->stream == SNDRV_PCM_STREAM_CAPTURE) {
>> +        bcm2835_i2s_calc_channel_pos(&rx_ch1_pos, &rx_ch2_pos,
>> +            rx_mask, slot_width, data_delay, odd_slot_offset);
>> +        regmap_write(dev->i2s_regmap, BCM2835_I2S_RXC_A_REG,
>> +              format
>> +            | BCM2835_I2S_CH1_POS(rx_ch1_pos)
>> +            | BCM2835_I2S_CH2_POS(rx_ch2_pos));
>> +    }
>> +
>> +    if (substream->stream == SNDRV_PCM_STREAM_PLAYBACK) {
>> +        bcm2835_i2s_calc_channel_pos(&tx_ch1_pos, &tx_ch2_pos,
>> +            tx_mask, slot_width, data_delay, odd_slot_offset);
>> +        regmap_write(dev->i2s_regmap, BCM2835_I2S_TXC_A_REG,
>> +              format
>> +            | BCM2835_I2S_CH1_POS(tx_ch1_pos)
>> +            | BCM2835_I2S_CH2_POS(tx_ch2_pos));
>> +    }
>>         /* Setup the I2S mode */