ptp: ptp_clock: make scaled_ppm_to_ppb static inline

Make scaled_ppm_to_ppb static inline to be able to build drivers that
use this function even with PTP_1588_CLOCK disabled.
Signed-off-by: Radu Pirea (NXP OSS) <radu-nicolae.pirea@oss.nxp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/ptp/ptp_clock.c

@@ -63,27 +63,6 @@ static void enqueue_external_timestamp(struct timestamp_event_queue *queue,
 	spin_unlock_irqrestore(&queue->lock, flags);
 }
 
-s32 scaled_ppm_to_ppb(long ppm)
-{
-	/*
-	 * The 'freq' field in the 'struct timex' is in parts per
-	 * million, but with a 16 bit binary fractional field.
-	 *
-	 * We want to calculate
-	 *
-	 *    ppb = scaled_ppm * 1000 / 2^16
-	 *
-	 * which simplifies to
-	 *
-	 *    ppb = scaled_ppm * 125 / 2^13
-	 */
-	s64 ppb = 1 + ppm;
-	ppb *= 125;
-	ppb >>= 13;
-	return (s32) ppb;
-}
-EXPORT_SYMBOL(scaled_ppm_to_ppb);
-
 /* posix clock implementation */
 
 static int ptp_clock_getres(struct posix_clock *pc, struct timespec64 *tp)

include/linux/ptp_clock_kernel.h

@@ -186,6 +186,32 @@ struct ptp_clock_event {
 	};
 };
 
+/**
+ * scaled_ppm_to_ppb() - convert scaled ppm to ppb
+ *
+ * @ppm:    Parts per million, but with a 16 bit binary fractional field
+ */
+static inline s32 scaled_ppm_to_ppb(long ppm)
+{
+	/*
+	 * The 'freq' field in the 'struct timex' is in parts per
+	 * million, but with a 16 bit binary fractional field.
+	 *
+	 * We want to calculate
+	 *
+	 *    ppb = scaled_ppm * 1000 / 2^16
+	 *
+	 * which simplifies to
+	 *
+	 *    ppb = scaled_ppm * 125 / 2^13
+	 */
+	s64 ppb = 1 + ppm;
+
+	ppb *= 125;
+	ppb >>= 13;
+	return (s32)ppb;
+}
+
 #if IS_REACHABLE(CONFIG_PTP_1588_CLOCK)
 
 /**
@@ -229,14 +255,6 @@ extern void ptp_clock_event(struct ptp_clock *ptp,
 
 extern int ptp_clock_index(struct ptp_clock *ptp);
 
-/**
- * scaled_ppm_to_ppb() - convert scaled ppm to ppb
- *
- * @ppm:    Parts per million, but with a 16 bit binary fractional field
- */
-
-extern s32 scaled_ppm_to_ppb(long ppm);
-
 /**
  * ptp_find_pin() - obtain the pin index of a given auxiliary function
  *