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

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Date:   Fri, 27 Mar 2020 10:56:50 +1100
From:   Matt Flax <flatmax@...tmax.org>
To:     unlisted-recipients:; (no To-header on input)
Cc:     Kate Stewart <kstewart@...uxfoundation.org>,
        alsa-devel@...a-project.org,
        Florian Fainelli <f.fainelli@...il.com>,
        linux-kernel@...r.kernel.org,
        Scott Branden <sbranden@...adcom.com>,
        Liam Girdwood <lgirdwood@...il.com>,
        linux-arm-kernel@...ts.infradead.org, Ray Jui <rjui@...adcom.com>,
        YueHaibing <yuehaibing@...wei.com>,
        Takashi Iwai <tiwai@...e.com>, Mark Brown <broonie@...nel.org>,
        bcm-kernel-feedback-list@...adcom.com,
        Allison Randal <allison@...utok.net>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Nicolas Saenz Julienne <nsaenzjulienne@...e.de>,
        linux-rpi-kernel@...ts.infradead.org
Subject: Re: [PATCH] ASoC: bcm2835-i2s: substream alignment now independent in
 hwparams


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@...tmax.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 */
>