[media] msi2500: 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/usb/msi2500/msi2500.c b/drivers/media/usb/msi2500/msi2500.c
index efc761c78f7250e5b27a93b0fcb18bbc3fb142a5..8605b96dc0b4b14aa3b4d81537cce070f70ace66 100644 (file)
--- a/drivers/media/usb/msi2500/msi2500.c
+++ b/drivers/media/usb/msi2500/msi2500.c
@@ -682,11 +682,10 @@ static int msi2500_ctrl_msg(struct msi2500_state *s, u8 cmd, u32 data)
        return ret;
 }
 
-#define F_REF 24000000
-#define DIV_R_IN 2
 static int msi2500_set_usb_adc(struct msi2500_state *s)
 {
-       int ret, div_n, div_m, div_r_out, f_sr, f_vco, fract;
+       int ret;
+       unsigned int f_vco, f_sr, div_n, k, k_cw, div_out;
        u32 reg3, reg4, reg7;
        struct v4l2_ctrl *bandwidth_auto;
        struct v4l2_ctrl *bandwidth;
@@ -727,6 +726,21 @@ static int msi2500_set_usb_adc(struct msi2500_state *s)
                break;
        }
 
+       /*
+        * Fractional-N synthesizer
+        *
+        *           +----------------------------------------+
+        *           v                                        |
+        *  Fref   +----+     +-------+     +-----+         +------+     +---+
+        * ------> | PD | --> |  VCO  | --> | /2  | ------> | /N.F | <-- | K |
+        *         +----+     +-------+     +-----+         +------+     +---+
+        *                      |
+        *                      |
+        *                      v
+        *                    +-------+     +-----+  Fout
+        *                    | /Rout | --> | /12 | ------>
+        *                    +-------+     +-----+
+        */
        /*
         * Synthesizer config is just a educated guess...
         *
@@ -754,10 +768,14 @@ static int msi2500_set_usb_adc(struct msi2500_state *s)
         *
         * VCO 202000000 - 720000000++
         */
+
+       #define F_REF 24000000
+       #define DIV_PRE_N 2
+       #define DIV_LO_OUT 12
        reg3 = 0x01000303;
        reg4 = 0x00000004;
 
-       /* XXX: Filters? AGC? */
+       /* XXX: Filters? AGC? VCO band? */
        if (f_sr < 6000000)
                reg3 |= 0x1 << 20;
        else if (f_sr < 7000000)
@@ -767,24 +785,25 @@ static int msi2500_set_usb_adc(struct msi2500_state *s)
        else
                reg3 |= 0xd << 20;
 
-       for (div_r_out = 4; div_r_out < 16; div_r_out += 2) {
-               f_vco = f_sr * div_r_out * 12;
-               dev_dbg(s->dev, "div_r_out=%d f_vco=%d\n", div_r_out, f_vco);
+       for (div_out = 4; div_out < 16; div_out += 2) {
+               f_vco = f_sr * div_out * DIV_LO_OUT;
+               dev_dbg(s->dev, "div_out=%d f_vco=%d\n", div_out, f_vco);
                if (f_vco >= 202000000)
                        break;
        }
 
-       div_n = f_vco / (F_REF * DIV_R_IN);
-       div_m = f_vco % (F_REF * DIV_R_IN);
-       fract = 0x200000ul * div_m / (F_REF * DIV_R_IN);
+       /* Calculate PLL integer and fractional control word. */
+       div_n = div_u64_rem(f_vco, DIV_PRE_N * F_REF, &k);
+       k_cw = div_u64((u64) k * 0x200000, DIV_PRE_N * F_REF);
 
        reg3 |= div_n << 16;
-       reg3 |= (div_r_out / 2 - 1) << 10;
-       reg3 |= ((fract >> 20) & 0x000001) << 15; /* [20] */
-       reg4 |= ((fract >>  0) & 0x0fffff) <<  8; /* [19:0] */
+       reg3 |= (div_out / 2 - 1) << 10;
+       reg3 |= ((k_cw >> 20) & 0x000001) << 15; /* [20] */
+       reg4 |= ((k_cw >>  0) & 0x0fffff) <<  8; /* [19:0] */
 
-       dev_dbg(s->dev, "f_sr=%d f_vco=%d div_n=%d div_m=%d div_r_out=%d reg3=%08x reg4=%08x\n",
-                       f_sr, f_vco, div_n, div_m, div_r_out, reg3, reg4);
+       dev_dbg(s->dev,
+               "f_sr=%u f_vco=%u div_n=%u k=%u div_out=%u reg3=%08x reg4=%08x\n",
+               f_sr, f_vco, div_n, k, div_out, reg3, reg4);
 
        ret = msi2500_ctrl_msg(s, CMD_WREG, 0x00608008);
        if (ret)