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SubjectRe: [PATCH] ASoC: bcm2835-i2s: substream alignment now independent in hwparams
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Should this patch be handled through the ALSA team the R. Pi team or the
BCM team ?


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@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 */
>

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