[media] msi001: revise synthesizer calculation

Update synthesizer calculation to model I prefer nowadays. It is mostly
just renaming some variables, but also minor functionality change how
integer and fractional part are divided (using div_u64_rem()). Also, add
'schematic' of synthesizer following my current understanding.

Signed-off-by: Antti Palosaari <crope@iki.fi>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>

diff --git a/drivers/media/tuners/msi001.c b/drivers/media/tuners/msi001.c
index 74cfc3c..d0ec4e3 100644 (file)
--- a/drivers/media/tuners/msi001.c
+++ b/drivers/media/tuners/msi001.c
@@ -91,15 +91,15 @@ err:
 static int msi001_set_tuner(struct msi001 *s)
 {
        int ret, i;
-       unsigned int n, m, thresh, frac, vco_step, tmp, f_if1;
+       unsigned int uitmp, div_n, k, k_thresh, k_frac, div_lo, f_if1;
        u32 reg;
-       u64 f_vco, tmp64;
-       u8 mode, filter_mode, lo_div;
+       u64 f_vco;
+       u8 mode, filter_mode;
 
        static const struct {
                u32 rf;
                u8 mode;
-               u8 lo_div;
+               u8 div_lo;
        } band_lut[] = {
                { 50000000, 0xe1, 16}, /* AM_MODE2, antenna 2 */
                {108000000, 0x42, 32}, /* VHF_MODE */
@@ -144,15 +144,15 @@ static int msi001_set_tuner(struct msi001 *s)
         */
        unsigned int f_if = 0;
        #define F_REF 24000000
-       #define R_REF 4
-       #define F_OUT_STEP 1
+       #define DIV_PRE_N 4
+       #define F_VCO_STEP div_lo
 
        dev_dbg(&s->spi->dev, "f_rf=%d f_if=%d\n", f_rf, f_if);
 
        for (i = 0; i < ARRAY_SIZE(band_lut); i++) {
                if (f_rf <= band_lut[i].rf) {
                        mode = band_lut[i].mode;
-                       lo_div = band_lut[i].lo_div;
+                       div_lo = band_lut[i].div_lo;
                        break;
                }
        }
@@ -200,32 +200,46 @@ static int msi001_set_tuner(struct msi001 *s)
 
        dev_dbg(&s->spi->dev, "bandwidth selected=%d\n", bandwidth_lut[i].freq);
 
-       f_vco = (u64) (f_rf + f_if + f_if1) * lo_div;
-       tmp64 = f_vco;
-       m = do_div(tmp64, F_REF * R_REF);
-       n = (unsigned int) tmp64;
+       /*
+        * Fractional-N synthesizer
+        *
+        *           +---------------------------------------+
+        *           v                                       |
+        *  Fref   +----+     +-------+         +----+     +------+     +---+
+        * ------> | PD | --> |  VCO  | ------> | /4 | --> | /N.F | <-- | K |
+        *         +----+     +-------+         +----+     +------+     +---+
+        *                      |
+        *                      |
+        *                      v
+        *                    +-------+  Fout
+        *                    | /Rout | ------>
+        *                    +-------+
+        */
 
-       vco_step = F_OUT_STEP * lo_div;
-       thresh = (F_REF * R_REF) / vco_step;
-       frac = 1ul * thresh * m / (F_REF * R_REF);
+       /* Calculate PLL integer and fractional control word. */
+       f_vco = (u64) (f_rf + f_if + f_if1) * div_lo;
+       div_n = div_u64_rem(f_vco, DIV_PRE_N * F_REF, &k);
+       k_thresh = (DIV_PRE_N * F_REF) / F_VCO_STEP;
+       k_frac = div_u64((u64) k * k_thresh, (DIV_PRE_N * F_REF));
 
        /* Find out greatest common divisor and divide to smaller. */
-       tmp = gcd(thresh, frac);
-       thresh /= tmp;
-       frac /= tmp;
+       uitmp = gcd(k_thresh, k_frac);
+       k_thresh /= uitmp;
+       k_frac /= uitmp;
 
        /* Force divide to reg max. Resolution will be reduced. */
-       tmp = DIV_ROUND_UP(thresh, 4095);
-       thresh = DIV_ROUND_CLOSEST(thresh, tmp);
-       frac = DIV_ROUND_CLOSEST(frac, tmp);
+       uitmp = DIV_ROUND_UP(k_thresh, 4095);
+       k_thresh = DIV_ROUND_CLOSEST(k_thresh, uitmp);
+       k_frac = DIV_ROUND_CLOSEST(k_frac, uitmp);
 
-       /* calc real RF set */
-       tmp = 1ul * F_REF * R_REF * n;
-       tmp += 1ul * F_REF * R_REF * frac / thresh;
-       tmp /= lo_div;
+       /* Calculate real RF set. */
+       uitmp = (unsigned int) F_REF * DIV_PRE_N * div_n;
+       uitmp += (unsigned int) F_REF * DIV_PRE_N * k_frac / k_thresh;
+       uitmp /= div_lo;
 
-       dev_dbg(&s->spi->dev, "rf=%u:%u n=%d thresh=%d frac=%d\n",
-                               f_rf, tmp, n, thresh, frac);
+       dev_dbg(&s->spi->dev,
+               "f_rf=%u:%u f_vco=%llu div_n=%u k_thresh=%u k_frac=%u div_lo=%u\n",
+               f_rf, uitmp, f_vco, div_n, k_thresh, k_frac, div_lo);
 
        ret = msi001_wreg(s, 0x00000e);
        if (ret)
@@ -246,7 +260,7 @@ static int msi001_set_tuner(struct msi001 *s)
                goto err;
 
        reg = 5 << 0;
-       reg |= thresh << 4;
+       reg |= k_thresh << 4;
        reg |= 1 << 19;
        reg |= 1 << 21;
        ret = msi001_wreg(s, reg);
@@ -254,8 +268,8 @@ static int msi001_set_tuner(struct msi001 *s)
                goto err;
 
        reg = 2 << 0;
-       reg |= frac << 4;
-       reg |= n << 16;
+       reg |= k_frac << 4;
+       reg |= div_n << 16;
        ret = msi001_wreg(s, reg);
        if (ret)
                goto err;
@@ -276,7 +290,7 @@ static int msi001_set_tuner(struct msi001 *s)
 err:
        dev_dbg(&s->spi->dev, "failed %d\n", ret);
        return ret;
-};
+}
 
 static int msi001_s_power(struct v4l2_subdev *sd, int on)
 {