mirror of https://gitee.com/openkylin/linux.git
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>
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@ -73,6 +73,39 @@ struct snd_platform_data {
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*/
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int clk_input_pin;
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/*
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* This flag works when both clock and FS are outputs for the cpu
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* and makes clock more accurate (FS is not symmetrical and the
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* clock is very fast.
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* The clock becoming faster is named
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* i2s continuous serial clock (I2S_SCK) and it is an externally
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* visible bit clock.
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*
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* first line : WordSelect
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* second line : ContinuousSerialClock
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* third line: SerialData
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*
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* SYMMETRICAL APPROACH:
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* _______________________ LEFT
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* _| RIGHT |______________________|
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* _ _ _ _ _ _ _ _
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* _| |_| |_ x16 _| |_| |_| |_| |_ x16 _| |_| |_
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* _ _ _ _ _ _ _ _
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* _/ \_/ \_ ... _/ \_/ \_/ \_/ \_ ... _/ \_/ \_
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* \_/ \_/ \_/ \_/ \_/ \_/ \_/ \_/
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*
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* ACCURATE CLOCK APPROACH:
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* ______________ LEFT
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* _| RIGHT |_______________________________|
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* _ _ _ _ _ _ _ _ _
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* _| |_ x16 _| |_| |_ x16 _| |_| |_| |_| |_| |_| |
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* _ _ _ _ dummy cycles
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* _/ \_ ... _/ \_/ \_ ... _/ \__________________
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* \_/ \_/ \_/ \_/
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*
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*/
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bool i2s_accurate_sck;
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/* McASP specific fields */
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int tdm_slots;
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u8 op_mode;
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@ -155,6 +155,7 @@ struct davinci_mcbsp_dev {
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unsigned int fmt;
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int clk_div;
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int clk_input_pin;
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bool i2s_accurate_sck;
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};
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static inline void davinci_mcbsp_write_reg(struct davinci_mcbsp_dev *dev,
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@ -447,11 +448,23 @@ static int davinci_i2s_hw_params(struct snd_pcm_substream *substream,
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DAVINCI_MCBSP_SRGR_CLKSM;
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srgr |= DAVINCI_MCBSP_SRGR_FWID(mcbsp_word_length *
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8 - 1);
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if (dev->i2s_accurate_sck) {
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clk_div = 256;
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do {
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framesize = (freq / (--clk_div)) /
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params->rate_num *
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params->rate_den;
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} while (((framesize < 33) || (framesize > 4095)) &&
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(clk_div));
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clk_div--;
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srgr |= DAVINCI_MCBSP_SRGR_FPER(framesize - 1);
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} else {
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/* symmetric waveforms */
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clk_div = freq / (mcbsp_word_length * 16) /
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params->rate_num * params->rate_den;
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srgr |= DAVINCI_MCBSP_SRGR_FPER(mcbsp_word_length *
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16 - 1);
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}
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clk_div &= 0xFF;
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srgr |= clk_div;
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break;
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@ -662,6 +675,7 @@ static int davinci_i2s_probe(struct platform_device *pdev)
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dev->dma_params[SNDRV_PCM_STREAM_CAPTURE].sram_size =
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pdata->sram_size_capture;
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dev->clk_input_pin = pdata->clk_input_pin;
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dev->i2s_accurate_sck = pdata->i2s_accurate_sck;
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}
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dev->clk = clk_get(&pdev->dev, NULL);
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if (IS_ERR(dev->clk)) {
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