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>

1 files changed, 33 insertions, 0 deletions

diff --git a/arch/arm/mach-davinci/include/mach/asp.h b/arch/arm/mach-davinci/include/mach/asp.h
index 0847d2144f1f..b12c69edeea5 100644
--- a/arch/arm/mach-davinci/include/mach/asp.h
+++ b/arch/arm/mach-davinci/include/mach/asp.h
@@ -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;