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>

1 files changed, 49 insertions, 26 deletions

diff --git a/sound/soc/codecs/tlv320aic3x.c b/sound/soc/codecs/tlv320aic3x.c
index 2b4dc2b0b017..5a8f53ce2250 100644
--- 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);