[alsa-devel] [PATCH] ASoC: bcm_2835: Simplify mono guard by returning error on mono
Matt Flax
flatmax at flatmax.org
Wed Mar 8 03:43:19 PST 2017
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.
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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