linux-kernel - Re: [PATCH 1/5] ASoC: sh: rz-ssi: Drop calling rz_ssi_pio

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Message-ID: <2f338a37-f2ca-33e4-284e-5d263f7b93da@intel.com>
Date:   Mon, 10 Jan 2022 16:48:30 +0100
From:   Cezary Rojewski <cezary.rojewski@...el.com>
To:     Lad Prabhakar <prabhakar.mahadev-lad.rj@...renesas.com>,
        Liam Girdwood <lgirdwood@...il.com>,
        Mark Brown <broonie@...nel.org>,
        Jaroslav Kysela <perex@...ex.cz>,
        Takashi Iwai <tiwai@...e.com>,
        Biju Das <biju.das.jz@...renesas.com>
CC:     Pavel Machek <pavel@...x.de>, <linux-renesas-soc@...r.kernel.org>,
        Prabhakar <prabhakar.csengg@...il.com>,
        <alsa-devel@...a-project.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/5] ASoC: sh: rz-ssi: Drop calling rz_ssi_pio_recv()
 recursively

On 2022-01-10 10:47 AM, Lad Prabhakar wrote:
> Instead of recursively calling rz_ssi_pio_recv() use a while loop
> to read the samples from RX fifo.

Recursion and loops are means for doing something repeatedly. Could you 
specify _why_ such change was made i.e. the conversion from one method 
into the other? I bet the code is not being changed for the sake of 
changing it, the reason is simply missing in the commit message.

Please note that refactoring below function into while-loop has a side 
effect: everything had to be indented by additional tab. Generally, 
readability increases if function is shaped 'linearly'.

> This also fixes an issue where the return value of rz_ssi_pio_recv()
> was ignored when called recursively.
> 
> Fixes: 03e786bd4341 ("ASoC: sh: Add RZ/G2L SSIF-2 driver")
> Reported-by: Pavel Machek <pavel@...x.de>
> Signed-off-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@...renesas.com>
> Reviewed-by: Biju Das <biju.das.jz@...renesas.com>
> ---
>   sound/soc/sh/rz-ssi.c | 68 ++++++++++++++++++++++---------------------
>   1 file changed, 35 insertions(+), 33 deletions(-)
> 
> diff --git a/sound/soc/sh/rz-ssi.c b/sound/soc/sh/rz-ssi.c
> index fa0cc08f70ec..37466f65c2b0 100644
> --- a/sound/soc/sh/rz-ssi.c
> +++ b/sound/soc/sh/rz-ssi.c
> @@ -411,54 +411,56 @@ static int rz_ssi_pio_recv(struct rz_ssi_priv *ssi, struct rz_ssi_stream *strm)
>   {
>   	struct snd_pcm_substream *substream = strm->substream;
>   	struct snd_pcm_runtime *runtime;
> +	bool done = false;
>   	u16 *buf;
>   	int fifo_samples;
>   	int frames_left;
> -	int samples = 0;
> +	int samples;
>   	int i;
>   
>   	if (!rz_ssi_stream_is_valid(ssi, strm))
>   		return -EINVAL;
>   
>   	runtime = substream->runtime;
> -	/* frames left in this period */
> -	frames_left = runtime->period_size - (strm->buffer_pos %
> -					      runtime->period_size);
> -	if (frames_left == 0)
> -		frames_left = runtime->period_size;
>   
> -	/* Samples in RX FIFO */
> -	fifo_samples = (rz_ssi_reg_readl(ssi, SSIFSR) >>
> -			SSIFSR_RDC_SHIFT) & SSIFSR_RDC_MASK;
> -
> -	/* Only read full frames at a time */
> -	while (frames_left && (fifo_samples >= runtime->channels)) {
> -		samples += runtime->channels;
> -		fifo_samples -= runtime->channels;
> -		frames_left--;
> -	}
> +	while (!done) {

I wonder if converting this into do-while isn't a better option. Maybe 
I'm missing something but 'done' flag seems to be changed only as an 
outcome of the last if-statement (last step) in this entire procedure. 
Perhaps condition from said if-statement could also be moved into 
'while' portion of do-while loop.

> +		/* frames left in this period */
> +		frames_left = runtime->period_size -
> +			      (strm->buffer_pos % runtime->period_size);
> +		if (!frames_left)
> +			frames_left = runtime->period_size;
> +
> +		/* Samples in RX FIFO */
> +		fifo_samples = (rz_ssi_reg_readl(ssi, SSIFSR) >>
> +				SSIFSR_RDC_SHIFT) & SSIFSR_RDC_MASK;
> +
> +		/* Only read full frames at a time */
> +		samples = 0;
> +		while (frames_left && (fifo_samples >= runtime->channels)) {
> +			samples += runtime->channels;
> +			fifo_samples -= runtime->channels;
> +			frames_left--;
> +		}
>   
> -	/* not enough samples yet */
> -	if (samples == 0)
> -		return 0;
> +		/* not enough samples yet */
> +		if (!samples)
> +			break;
>   
> -	/* calculate new buffer index */
> -	buf = (u16 *)(runtime->dma_area);
> -	buf += strm->buffer_pos * runtime->channels;
> +		/* calculate new buffer index */
> +		buf = (u16 *)(runtime->dma_area);

Is the second pair of brackets needed?

> +		buf += strm->buffer_pos * runtime->channels;
>   
> -	/* Note, only supports 16-bit samples */
> -	for (i = 0; i < samples; i++)
> -		*buf++ = (u16)(rz_ssi_reg_readl(ssi, SSIFRDR) >> 16);
> +		/* Note, only supports 16-bit samples */
> +		for (i = 0; i < samples; i++)
> +			*buf++ = (u16)(rz_ssi_reg_readl(ssi, SSIFRDR) >> 16);
>   
> -	rz_ssi_reg_mask_setl(ssi, SSIFSR, SSIFSR_RDF, 0);
> -	rz_ssi_pointer_update(strm, samples / runtime->channels);
> +		rz_ssi_reg_mask_setl(ssi, SSIFSR, SSIFSR_RDF, 0);
> +		rz_ssi_pointer_update(strm, samples / runtime->channels);
>   
> -	/*
> -	 * If we finished this period, but there are more samples in
> -	 * the RX FIFO, call this function again
> -	 */
> -	if (frames_left == 0 && fifo_samples >= runtime->channels)
> -		rz_ssi_pio_recv(ssi, strm);
> +		/* check if there are no more samples in the RX FIFO */
> +		if (!(!frames_left && fifo_samples >= runtime->channels))
> +			done = true;
> +	}
>   
>   	return 0;
>   }
>