ASoC: PLL computation in TLV320AIC3x SoC driver

fix precision of PLL computation for TLV320AIC3x SoC driver,
test results are at http://pmeerw.net/clk

Signed-off-by: Peter Meerwald <pmeerw@pmeerw.net>
Acked-by: Vladimir Barinov <vova.barinov@gmail.com>
Acked-by: Liam Girdwood <lrg@slimlogic.co.uk>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>

diff --git a/sound/soc/codecs/tlv320aic3x.c b/sound/soc/codecs/tlv320aic3x.c
index 2b4dc2b0b01724aa91507e330860d9d7bc7e0eda..5a8f53ce22500fbebcc4cae433ac53e1550fd2f2 100644 (file)
--- a/sound/soc/codecs/tlv320aic3x.c
+++ b/sound/soc/codecs/tlv320aic3x.c
@@ -765,9 +765,10 @@ static int aic3x_hw_params(struct snd_pcm_substream *substream,
        struct snd_soc_codec *codec = socdev->card->codec;
        struct aic3x_priv *aic3x = codec->private_data;
        int codec_clk = 0, bypass_pll = 0, fsref, last_clk = 0;
-       u8 data, r, p, pll_q, pll_p = 1, pll_r = 1, pll_j = 1;
-       u16 pll_d = 1;
+       u8 data, j, r, p, pll_q, pll_p = 1, pll_r = 1, pll_j = 1;
+       u16 d, pll_d = 1;
        u8 reg;
+       int clk;
 
        /* select data word length */
        data =
@@ -833,48 +834,70 @@ static int aic3x_hw_params(struct snd_pcm_substream *substream,
        if (bypass_pll)
                return 0;
 
-       /* Use PLL
-        * find an apropriate setup for j, d, r and p by iterating over
-        * p and r - j and d are calculated for each fraction.
-        * Up to 128 values are probed, the closest one wins the game.
+       /* Use PLL, compute apropriate setup for j, d, r and p, the closest
+        * one wins the game. Try with d==0 first, next with d!=0.
+        * Constraints for j are according to the datasheet.
         * The sysclk is divided by 1000 to prevent integer overflows.
         */
+
        codec_clk = (2048 * fsref) / (aic3x->sysclk / 1000);
 
        for (r = 1; r <= 16; r++)
                for (p = 1; p <= 8; p++) {
-                       int clk, tmp = (codec_clk * pll_r * 10) / pll_p;
-                       u8 j = tmp / 10000;
-                       u16 d = tmp % 10000;
+                       for (j = 4; j <= 55; j++) {
+                               /* This is actually 1000*((j+(d/10000))*r)/p
+                                * The term had to be converted to get
+                                * rid of the division by 10000; d = 0 here
+                                */
+                               int clk = (1000 * j * r) / p;
+
+                               /* Check whether this values get closer than
+                                * the best ones we had before
+                                */
+                               if (abs(codec_clk - clk) <
+                                       abs(codec_clk - last_clk)) {
+                                       pll_j = j; pll_d = 0;
+                                       pll_r = r; pll_p = p;
+                                       last_clk = clk;
+                               }
+
+                               /* Early exit for exact matches */
+                               if (clk == codec_clk)
+                                       goto found;
+                       }
+               }
 
-                       if (j > 63)
-                               continue;
+       /* try with d != 0 */
+       for (p = 1; p <= 8; p++) {
+               j = codec_clk * p / 1000;
 
-                       if (d != 0 && aic3x->sysclk < 10000000)
-                               continue;
+               if (j < 4 || j > 11)
+                       continue;
 
-                       /* This is actually 1000 * ((j + (d/10000)) * r) / p
-                        * The term had to be converted to get rid of the
-                        * division by 10000 */
-                       clk = ((10000 * j * r) + (d * r)) / (10 * p);
+               /* do not use codec_clk here since we'd loose precision */
+               d = ((2048 * p * fsref) - j * aic3x->sysclk)
+                       * 100 / (aic3x->sysclk/100);
 
-                       /* check whether this values get closer than the best
-                        * ones we had before */
-                       if (abs(codec_clk - clk) < abs(codec_clk - last_clk)) {
-                               pll_j = j; pll_d = d; pll_r = r; pll_p = p;
-                               last_clk = clk;
-                       }
+               clk = (10000 * j + d) / (10 * p);
 
-                       /* Early exit for exact matches */
-                       if (clk == codec_clk)
-                               break;
+               /* check whether this values get closer than the best
+                * ones we had before */
+               if (abs(codec_clk - clk) < abs(codec_clk - last_clk)) {
+                       pll_j = j; pll_d = d; pll_r = 1; pll_p = p;
+                       last_clk = clk;
                }
 
+               /* Early exit for exact matches */
+               if (clk == codec_clk)
+                       goto found;
+       }
+
        if (last_clk == 0) {
                printk(KERN_ERR "%s(): unable to setup PLL\n", __func__);
                return -EINVAL;
        }
 
+found:
        data = aic3x_read_reg_cache(codec, AIC3X_PLL_PROGA_REG);
        aic3x_write(codec, AIC3X_PLL_PROGA_REG, data | (pll_p << PLLP_SHIFT));
        aic3x_write(codec, AIC3X_OVRF_STATUS_AND_PLLR_REG, pll_r << PLLR_SHIFT);