Commit d9823ed9 authored by Raffaele Recalcati's avatar Raffaele Recalcati Committed by Mark Brown
Browse files

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: default avatarRaffaele Recalcati <raffaele.recalcati@bticino.it>
Signed-off-by: default avatarDavide Bonfanti <davide.bonfanti@bticino.it>
Acked-by: default avatarLiam Girdwood <lrg@slimlogic.co.uk>
Acked-by: default avatarSudhakar Rajashekhara <sudhakar.raj@ti.com>
Signed-off-by: default avatarMark Brown <broonie@opensource.wolfsonmicro.com>
parent ec637553

arch/arm/mach-davinci/include/mach/asp.h

+33 −0
Original line number Diff line number Diff line
@@ -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;

sound/soc/davinci/davinci-i2s.c

+19 −5
Original line number Diff line number Diff line
@@ -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);

		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)) {

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