powerpc/5200: add function to return external clock frequency

This patch adds the utility function mpc52xx_get_xtal_freq() to get
the frequency of the external oscillator clock connected to the pin
SYS_XTAL_IN. The MSCAN may us it as clock source. Unfortunately, this
value is not available from the FDT blob, but it can be determined
from the IPB frequency.

Signed-off-by: Wolfgang Grandegger <wg@grandegger.com>
Signed-off-by: Grant Likely <grant.likely@secretlab.ca>

arch/powerpc/include/asm/mpc52xx.h

@@ -273,6 +273,7 @@ extern void mpc5200_setup_xlb_arbiter(void);
 extern void mpc52xx_declare_of_platform_devices(void);
 extern void mpc52xx_map_common_devices(void);
 extern int mpc52xx_set_psc_clkdiv(int psc_id, int clkdiv);
+extern unsigned int mpc52xx_get_xtal_freq(struct device_node *node);
 extern void mpc52xx_restart(char *cmd);
 
 /* mpc52xx_pic.c */

arch/powerpc/platforms/52xx/mpc52xx_common.c

@@ -205,6 +205,43 @@ int mpc52xx_set_psc_clkdiv(int psc_id, int clkdiv)
 }
 EXPORT_SYMBOL(mpc52xx_set_psc_clkdiv);
 
+/**
+ * mpc52xx_get_xtal_freq - Get SYS_XTAL_IN frequency for a device
+ *
+ * @node: device node
+ *
+ * Returns the frequency of the external oscillator clock connected
+ * to the SYS_XTAL_IN pin, or 0 if it cannot be determined.
+ */
+unsigned int mpc52xx_get_xtal_freq(struct device_node *node)
+{
+	u32 val;
+	unsigned int freq;
+
+	if (!mpc52xx_cdm)
+		return 0;
+
+	freq = mpc52xx_find_ipb_freq(node);
+	if (!freq)
+		return 0;
+
+	if (in_8(&mpc52xx_cdm->ipb_clk_sel) & 0x1)
+		freq *= 2;
+
+	val  = in_be32(&mpc52xx_cdm->rstcfg);
+	if (val & (1 << 5))
+		freq *= 8;
+	else
+		freq *= 4;
+	if (val & (1 << 6))
+		freq /= 12;
+	else
+		freq /= 16;
+
+	return freq;
+}
+EXPORT_SYMBOL(mpc52xx_get_xtal_freq);
+
 /**
  * mpc52xx_restart: ppc_md->restart hook for mpc5200 using the watchdog timer
  */