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ASoC: DaVinci: More accurate continuous serial clock for McBSP (I2S) 

i2s_accurate_sck switch can be used to have a better approximate
    sampling frequency.
    The clock is an externally visible bit clock and it is named
    i2s continuous serial clock (I2S_SCK).
    The trade off is between more accurate clock (fast clock)
    and less accurate clock (slow clock).
    The waveform will be not symmetric.
    Probably it is possible to get a better algorithm for calculating
    the divider, trying to keep a slower clock as possible.

    This patch has been developed against the
        http://git.kernel.org/pub/scm/linux/kernel/git/khilman/linux-davinci.git
    git tree and has been tested on bmx board (similar to dm365 evm, but using
    uda1345 as external audio codec).

Signed-off-by: Raffaele Recalcati <raffaele.recalcati@bticino.it>
Signed-off-by: Davide Bonfanti <davide.bonfanti@bticino.it>
Acked-by: Liam Girdwood <lrg@slimlogic.co.uk>
Acked-by: Sudhakar Rajashekhara <sudhakar.raj@ti.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
This commit is contained in:
Raffaele Recalcati 2010-07-06 10:39:04 +02:00 committed by Mark Brown
parent ec63755337
commit d9823ed9fa
2 changed files with 52 additions and 5 deletions
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33
arch/arm/mach-davinci/include/mach/asp.h
View File

@ -73,6 +73,39 @@ struct snd_platform_data {
*/
int clk_input_pin;
/*
* This flag works when both clock and FS are outputs for the cpu
* and makes clock more accurate (FS is not symmetrical and the
* clock is very fast.
* The clock becoming faster is named
* i2s continuous serial clock (I2S_SCK) and it is an externally
* visible bit clock.
*
* first line : WordSelect
* second line : ContinuousSerialClock
* third line: SerialData
*
* SYMMETRICAL APPROACH:
* _______________________ LEFT
* _| RIGHT |______________________|
* _ _ _ _ _ _ _ _
* _| |_| |_ x16 _| |_| |_| |_| |_ x16 _| |_| |_
* _ _ _ _ _ _ _ _
* _/ \_/ \_ ... _/ \_/ \_/ \_/ \_ ... _/ \_/ \_
* \_/ \_/ \_/ \_/ \_/ \_/ \_/ \_/
*
* ACCURATE CLOCK APPROACH:
* ______________ LEFT
* _| RIGHT |_______________________________|
* _ _ _ _ _ _ _ _ _
* _| |_ x16 _| |_| |_ x16 _| |_| |_| |_| |_| |_| |
* _ _ _ _ dummy cycles
* _/ \_ ... _/ \_/ \_ ... _/ \__________________
* \_/ \_/ \_/ \_/
*
*/
bool i2s_accurate_sck;
/* McASP specific fields */
int tdm_slots;
u8 op_mode;

24
sound/soc/davinci/davinci-i2s.c
View File

@ -155,6 +155,7 @@ struct davinci_mcbsp_dev {
unsigned int fmt;
int clk_div;
int clk_input_pin;
bool i2s_accurate_sck;
};
static inline void davinci_mcbsp_write_reg(struct davinci_mcbsp_dev *dev,
@ -447,11 +448,23 @@ static int davinci_i2s_hw_params(struct snd_pcm_substream *substream,
DAVINCI_MCBSP_SRGR_CLKSM;
srgr |= DAVINCI_MCBSP_SRGR_FWID(mcbsp_word_length *
8 - 1);
/* symmetric waveforms */
clk_div = freq / (mcbsp_word_length * 16) /
params->rate_num * params->rate_den;
srgr |= DAVINCI_MCBSP_SRGR_FPER(mcbsp_word_length *
16 - 1);
if (dev->i2s_accurate_sck) {
clk_div = 256;
do {
framesize = (freq / (--clk_div)) /
params->rate_num *
params->rate_den;
} while (((framesize < 33) || (framesize > 4095)) &&
(clk_div));
clk_div--;
srgr |= DAVINCI_MCBSP_SRGR_FPER(framesize - 1);
} else {
/* symmetric waveforms */
clk_div = freq / (mcbsp_word_length * 16) /
params->rate_num * params->rate_den;
srgr |= DAVINCI_MCBSP_SRGR_FPER(mcbsp_word_length *
16 - 1);
}
clk_div &= 0xFF;
srgr |= clk_div;
break;
@ -662,6 +675,7 @@ static int davinci_i2s_probe(struct platform_device *pdev)
dev->dma_params[SNDRV_PCM_STREAM_CAPTURE].sram_size =
pdata->sram_size_capture;
dev->clk_input_pin = pdata->clk_input_pin;
dev->i2s_accurate_sck = pdata->i2s_accurate_sck;
}
dev->clk = clk_get(&pdev->dev, NULL);
if (IS_ERR(dev->clk)) {