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bcm2835-i2s: Changes for allowing asymmetric sample formats. #1783

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Merged
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Jan 10, 2017
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bcm2835-i2s: Changes for allowing asymmetric sample formats. #1783

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54 changes: 38 additions & 16 deletions sound/soc/bcm/bcm2835-i2s.c
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Original file line number Diff line number Diff line change
Expand Up @@ -310,6 +310,7 @@ static int bcm2835_i2s_hw_params(struct snd_pcm_substream *substream,
unsigned int sampling_rate = params_rate(params);
unsigned int data_length, data_delay, bclk_ratio;
unsigned int ch1pos, ch2pos, mode, format;
unsigned int previous_ftxp, previous_frxp;
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These are still unnecessary.

unsigned int mash = BCM2835_CLK_MASH_1;
unsigned int divi, divf, target_frequency;
int clk_src = -1;
Expand All @@ -320,6 +321,7 @@ static int bcm2835_i2s_hw_params(struct snd_pcm_substream *substream,
bool frame_master = (master == SND_SOC_DAIFMT_CBS_CFS
|| master == SND_SOC_DAIFMT_CBM_CFS);
uint32_t csreg;
bool packed;

/*
* If a stream is already enabled,
Expand Down Expand Up @@ -465,26 +467,46 @@ static int bcm2835_i2s_hw_params(struct snd_pcm_substream *substream,
return -EINVAL;
}

/*
* Set format for both streams.
* We cannot set another frame length
* (and therefore word length) anyway,
* so the format will be the same.
*/
regmap_write(dev->i2s_regmap, BCM2835_I2S_RXC_A_REG, format);
regmap_write(dev->i2s_regmap, BCM2835_I2S_TXC_A_REG, format);
/* Set the format for the matching stream direction. */
switch (substream->stream) {
case SNDRV_PCM_STREAM_PLAYBACK:
regmap_write(dev->i2s_regmap, BCM2835_I2S_TXC_A_REG, format);
break;
case SNDRV_PCM_STREAM_CAPTURE:
regmap_write(dev->i2s_regmap, BCM2835_I2S_RXC_A_REG, format);
break;
default:
return -EINVAL;
}
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The format is the same, why split ?

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hw_params is called once for each direction (playback, capture), depending on what the user software wants to do. The substream->stream stores the requested direction. So the whole idea of this pull request is to react and change only the state that is relevant to the requested direction.

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OK seems good.


/* Setup the I2S mode */
/* Keep existing FTXP and FRXP values. */
regmap_read(dev->i2s_regmap, BCM2835_I2S_MODE_A_REG, &mode);
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The implications of restoring the mode are quite large and risky! Why not let the file set it up from scratch ?
All the lines which treat mode in the file do "mode |=" to alter mode. They all assume that mode starts as : mode = 0;

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Only the stream direction specific state is kept, not the whole mode.

There's mode = 0 line still there, see below.

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Yep I see it now.


previous_ftxp = mode & BCM2835_I2S_FTXP;
previous_frxp = mode & BCM2835_I2S_FRXP;
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If these previous variables aren't used, they should be removed.

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They are used, see below.

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These can still be removed, see my new comment for line number 502


mode = 0;
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Here the mode is reset.

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@flatmax flatmax Jan 10, 2017 •
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Yep, I see, but you can get rid of this for simplification because of changes suggested from line 502


if (data_length <= 16) {
/*
* Use frame packed mode (2 channels per 32 bit word)
* We cannot set another frame length in the second stream
* (and therefore word length) anyway,
* so the format will be the same.
*/
mode |= BCM2835_I2S_FTXP | BCM2835_I2S_FRXP;
/*
* Retain the frame packed mode (2 channels per 32 bit word)
* of the other direction stream intact. The formats of each
* direction can be different as long as the frame length is
* shared for both.
*/
packed = data_length <= 16;
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Not sure if it is good practice, but the packed variable can also be removed and this can be inline below.


switch (substream->stream) {
case SNDRV_PCM_STREAM_PLAYBACK:
mode |= previous_frxp;
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@gtrainavicius gtrainavicius Jan 10, 2017 •
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This is the location where previous_... variables are used.

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@flatmax flatmax Jan 10, 2017 •
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Oh yep, however you can remove this line, not necessary.

mode |= packed ? BCM2835_I2S_FTXP : 0;
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Replace this with : mode &= packed ? BCM2835_I2S_FTXP : 0;

break;
case SNDRV_PCM_STREAM_CAPTURE:
mode |= previous_ftxp;
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@flatmax flatmax Jan 10, 2017 •
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Remove this line.

mode |= packed ? BCM2835_I2S_FRXP : 0;
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Replace this with : mode &= packed ? BCM2835_I2S_FRXP : 0;

break;
default:
return -EINVAL;
}

mode |= BCM2835_I2S_FLEN(bclk_ratio - 1);
Expand Down