[alsa-devel] [PATCH] ASoC: bcm_2835: Simplify mono guard by returning error on mono

[Matthias Reichl]

On Wed, Mar 08, 2017 at 10:43:19PM +1100, Matt Flax wrote:
> 
> 
> On 08/03/17 22:33, Matthias Reichl wrote:
> >On Wed, Mar 08, 2017 at 09:58:54PM +1100, Matt Flax wrote:
> >>This patch simplifies the bcm2835_i2s.c code when the driver returns
> >>error on mono channel requests. It does this by testing for mono
> >>instead of using a switch statement to test for stereo.
> >>
> >>The bcm2835_i2s driver can only work in stereo mode. Whilst leaving
> >>the driver entirel compliant with the I2S protocol, it simplifies the
> >>code by removing a few redundant lines of code.
> >>
> >>Signed-off-by: Matt Flax <flatmax at flatmax.org>
> >I'm against this, it removes the semantics that I2S can only do 2
> >channels from the code part. Without looking at the rest of the code
> >one could get the impression that bcm2835-i2s could support all
> >layouts except 1 channel.
> >
> 
> The comment clearly states :
> 
> 	/*
> 	 * Check we aren't setting channel 2 on a mono stream.
> 	 * We currently only support stereo
> 	 */
> 
> How could anyone possibly think that it would support  "all layouts except 1
> channel" ?
> 
> I have reduced the clock cycle count to implement the same logic in code. I
> have clearly indicated that we ONLY support stereo channel counts.
> 
> In my opinion this code is simpler, easier to read and makes more sense.

In the current implementation this is obvious without looking into
comments.

It's also odd that you write "We currently only support stereo"
in the comments but then implement a "fail on channels == 1".

If you want to simplify the code and keep it readable you could
do it this way - this also preserves semantics of the code:

/* Only stereo is supported - but this is obvious and the comment can be removed */
if (params_channels(params) != 2)
	return -EINVAL;

I don't see a pressing need to change to the current upstream
driver, the code is fine and readable as well.

so long,

Hias

> 
> thanks
> Matt
> 
> 
> >>---
> >>  sound/soc/bcm/bcm2835-i2s.c | 17 +++++++++--------
> >>  1 file changed, 9 insertions(+), 8 deletions(-)
> >>
> >>diff --git a/sound/soc/bcm/bcm2835-i2s.c b/sound/soc/bcm/bcm2835-i2s.c
> >>index 6ba2049..1e6a1da 100644
> >>--- a/sound/soc/bcm/bcm2835-i2s.c
> >>+++ b/sound/soc/bcm/bcm2835-i2s.c
> >>@@ -310,15 +310,16 @@ static int bcm2835_i2s_hw_params(struct snd_pcm_substream *substream,
> >>  	ch1pos = data_delay;
> >>  	ch2pos = bclk_ratio / 2 + data_delay;
> >>-	switch (params_channels(params)) {
> >>-	case 2:
> >>-		format = BCM2835_I2S_CH1(format) | BCM2835_I2S_CH2(format);
> >>-		format |= BCM2835_I2S_CH1(BCM2835_I2S_CHPOS(ch1pos));
> >>-		format |= BCM2835_I2S_CH2(BCM2835_I2S_CHPOS(ch2pos));
> >>-		break;
> >>-	default:
> >>+	/* C
> >>+	 * Check we aren't setting channel 2 on a mono stream.
> >>+	 * We currently only support stereo
> >>+	 */
> >>+	if (params_channels(params) == 1)
> >>  		return -EINVAL;
> >>-	}
> >>+
> >>+	format = BCM2835_I2S_CH1(format) | BCM2835_I2S_CH2(format);
> >>+	format |= BCM2835_I2S_CH1(BCM2835_I2S_CHPOS(ch1pos));
> >>+	format |= BCM2835_I2S_CH2(BCM2835_I2S_CHPOS(ch2pos));
> >>  	/*
> >>  	 * Set format for both streams.
> >>-- 
> >>2.7.4
> >>
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