V4L/DVB (6245): GemTek Radio card - frequency calculation

Frequency calculation to use better math.  It's still the same
IF offset and step size (which are not the same as the datasheet says) as
the code was before.  It's just more efficient and accurate.
Signed-off-by: Trent Piepho <xyzzy@speakeasy.org>
Reviewed-by: Pekka Seppänen <pexu@kapsi.fi>
Signed-off-by: Douglas Schilling Landgraf <dougsland@gmail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>

drivers/media/radio/radio-gemtek.c

@@ -89,6 +89,14 @@ module_param(radio_nr, int, 0444);
 #define GEMTEK_LOWFREQ	(87*16000)
 #define GEMTEK_HIGHFREQ	(108*16000)
 
+/*
+ * Frequency calculation constants.  Intermediate frequency 10.52 MHz (nominal
+ * value 10.7 MHz), reference divisor 6.39 kHz (nominal 6.25 kHz).
+ */
+#define FSCALE		8
+#define IF_OFFSET	((unsigned int)(10.52 * 16000 * (1<<FSCALE)))
+#define REF_FREQ	((unsigned int)(6.39 * 16 * (1<<FSCALE)))
+
 #define GEMTEK_CK		0x01	/* Clock signal			*/
 #define GEMTEK_DA		0x02	/* Serial data			*/
 #define GEMTEK_CE		0x04	/* Chip enable			*/
@@ -219,14 +227,11 @@ static void gemtek_bu2614_transmit(struct gemtek_device *dev)
 }
 
 /*
- * Convert FM-frequency for BU2614FS (3.125 KHz STDF expected).
+ * Calculate divisor from FM-frequency for BU2614FS (3.125 KHz STDF expected).
  */
-static inline void gemtek_convfreq(unsigned long *freq)
+static unsigned long gemtek_convfreq(unsigned long freq)
 {
-	(*freq) /= 160;
-	(*freq) += 1052;	/* FMIN, 10.52 MHz		*/
-	(*freq) *= 1565;	/* STDF, 1 / 156.5 = 0.00639	*/
-	(*freq) /= 1000;
+	return ((freq<<FSCALE) + IF_OFFSET + REF_FREQ/2) / REF_FREQ;
 }
 
 /*
@@ -253,10 +258,8 @@ static void gemtek_setfreq(struct gemtek_device *dev, unsigned long freq)
 	gemtek_bu2614_set(dev, BU2614_FMUN, 1);	/* GT bit set	*/
 	gemtek_bu2614_set(dev, BU2614_TEST, 0);
 
-	gemtek_convfreq(&freq);
-
 	gemtek_bu2614_set(dev, BU2614_STDF, GEMTEK_STDF_3_125_KHZ);
-	gemtek_bu2614_set(dev, BU2614_FREQ, freq);
+	gemtek_bu2614_set(dev, BU2614_FREQ, gemtek_convfreq(freq));
 
 	gemtek_bu2614_transmit(dev);
 }