can: mcp251xfd: mcp251xfd_chip_wait_for_osc_ready(): prepare for PLL support

The function mcp251xfd_chip_wait_for_osc_ready() polls the Oscillator
Control Register for the oscillator to get ready. By passing the
appropriate parameters (osc_reference and osc_mask) it can also poll
for PLL ready.

This patch adjusts the error message if the Oscillator and/or PLL fail
to get ready.

Link: https://lore.kernel.org/all/20220207131047.282110-9-mkl@pengutronix.deSigned-off-by: Marc Kleine-Budde <mkl@pengutronix.de>

drivers/net/can/spi/mcp251xfd/mcp251xfd-core.c

@@ -112,6 +112,22 @@ static const char *mcp251xfd_get_mode_str(const u8 mode)
 	return "<unknown>";
 }
 
+static const char *
+mcp251xfd_get_osc_str(const u32 osc, const u32 osc_reference)
+{
+	switch (~osc & osc_reference &
+		(MCP251XFD_REG_OSC_OSCRDY | MCP251XFD_REG_OSC_PLLRDY)) {
+	case MCP251XFD_REG_OSC_PLLRDY:
+		return "PLL";
+	case MCP251XFD_REG_OSC_OSCRDY:
+		return "Oscillator";
+	case MCP251XFD_REG_OSC_PLLRDY | MCP251XFD_REG_OSC_OSCRDY:
+		return "Oscillator/PLL";
+	}
+
+	return "<unknown>";
+}
+
 static inline int mcp251xfd_vdd_enable(const struct mcp251xfd_priv *priv)
 {
 	if (!priv->reg_vdd)
@@ -269,8 +285,9 @@ mcp251xfd_chip_wait_for_osc_ready(const struct mcp251xfd_priv *priv,
 	}
 
 	netdev_err(priv->ndev,
-		   "Timeout waiting for Oscillator Ready (osc=0x%08x, osc_reference=0x%08x)\n",
-		   osc, osc_reference);
+		   "Timeout waiting for %s ready (osc=0x%08x, osc_reference=0x%08x, osc_mask=0x%08x).\n",
+		   mcp251xfd_get_osc_str(osc, osc_reference),
+		   osc, osc_reference, osc_mask);
 
 	return -ETIMEDOUT;
 }
@@ -298,6 +315,10 @@ static int mcp251xfd_chip_clock_enable(const struct mcp251xfd_priv *priv)
 	if (err)
 		return err;
 
+	/* Sometimes the PLL is stuck enabled, the controller never
+	 * sets the OSC Ready bit, and we get an -ETIMEDOUT. Our
+	 * caller takes care of retry.
+	 */
 	return mcp251xfd_chip_wait_for_osc_ready(priv, osc_reference, osc_mask);
 }