can: mcp251xfd: mcp251xfd_chip_wait_for_osc_ready(): improve chip detection and error handling

The function mcp251xfd_chip_wait_for_osc_ready() polls the Oscillator
Control Register for the oscillator to get ready.

This is the first register the driver reads from. Reading implausible
values (all bits set or unset) can be caused by the chip starting up
after power on, waking up after sleep, or by the chip not being preset
at all. Add check for implausible register content
mcp251xfd_reg_invalid() to the regmap_read_poll_timeout() loop.

In case of a regmap_read_poll_timeout() returns a fatal error (and not
a timeout), forward it to the caller.

As mcp251xfd_chip_wait_for_osc_ready() will be called after the probe
function has finished, (currently during ifup), move error message
about failed chip detection from there into the probe function.

Link: https://lore.kernel.org/all/20220207131047.282110-8-mkl@pengutronix.deSigned-off-by: Marc Kleine-Budde <mkl@pengutronix.de>

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

@@ -254,22 +254,25 @@ mcp251xfd_chip_wait_for_osc_ready(const struct mcp251xfd_priv *priv,
 	int err;
 
 	err = regmap_read_poll_timeout(priv->map_reg, MCP251XFD_REG_OSC, osc,
+				       !mcp251xfd_reg_invalid(osc) &&
 				       (osc & osc_mask) == osc_reference,
 				       MCP251XFD_OSC_STAB_SLEEP_US,
 				       MCP251XFD_OSC_STAB_TIMEOUT_US);
+	if (err != -ETIMEDOUT)
+		return err;
+
 	if (mcp251xfd_reg_invalid(osc)) {
 		netdev_err(priv->ndev,
-			   "Failed to detect %s (osc=0x%08x).\n",
-			   mcp251xfd_get_model_str(priv), osc);
+			   "Failed to read Oscillator Configuration Register (osc=0x%08x).\n",
+			   osc);
 		return -ENODEV;
-	} else if (err == -ETIMEDOUT) {
+	}
+
 	netdev_err(priv->ndev,
 		   "Timeout waiting for Oscillator Ready (osc=0x%08x, osc_reference=0x%08x)\n",
 		   osc, osc_reference);
-		return -ETIMEDOUT;
-	}
 
-	return 0;
+	return -ETIMEDOUT;
 }
 
 static int mcp251xfd_chip_clock_enable(const struct mcp251xfd_priv *priv)
@@ -1965,8 +1968,11 @@ static int mcp251xfd_probe(struct spi_device *spi)
 		goto out_free_candev;
 
 	err = mcp251xfd_register(priv);
-	if (err)
+	if (err) {
+		dev_err_probe(&spi->dev, err, "Failed to detect %s.\n",
+			      mcp251xfd_get_model_str(priv));
 		goto out_can_rx_offload_del;
+	}
 
 	return 0;