misc: rp1-pio: Defer for out-of-order probing

In the event that a client of the rp1-pio driver is probed before it,
return -EPROBE_DEFER from pio_open to allow it to be retried.
Otherwise, return an error code on error, not a NULL pointer, as that
is what clients are expecting.

See: raspberrypi#7211

Signed-off-by: Phil Elwell <phil@raspberrypi.com>

Author: pelwell

drivers/misc/rp1-pio.c

@@ -1035,7 +1035,9 @@ struct rp1_pio_client *rp1_pio_open(void)
 	struct rp1_pio_client *client;
 
 	if (!g_pio)
-		return ERR_PTR(-ENOENT);
+		return ERR_PTR(-EPROBE_DEFER);
+	if (IS_ERR(g_pio))
+		return ERR_CAST(g_pio);
 
 	client = kzalloc(sizeof(*client), GFP_KERNEL);
 	if (!client)
@@ -1292,15 +1294,18 @@ static int rp1_pio_probe(struct platform_device *pdev)
 		return dev_err_probe(dev, -EPROBE_DEFER, "failed to find RP1 firmware driver\n");
 	if (IS_ERR(fw)) {
 		dev_warn(dev, "failed to contact RP1 firmware\n");
-		return PTR_ERR(fw);
+		ret = PTR_ERR(fw);
+		goto out_err;
 	}
 	ret = rp1_firmware_get_feature(fw, FOURCC_PIO, &op_base, &op_count);
 	if (ret < 0)
-		return ret;
+		goto out_err;
 
 	pio = devm_kzalloc(&pdev->dev, sizeof(*pio), GFP_KERNEL);
-	if (!pio)
-		return -ENOMEM;
+	if (!pio) {
+		ret = -ENOMEM;
+		goto out_err;
+	}
 
 	platform_set_drvdata(pdev, pio);
 	pio->fw_pio_base = op_base;
@@ -1311,8 +1316,10 @@ static int rp1_pio_probe(struct platform_device *pdev)
 	mutex_init(&pio->instr_mutex);
 
 	p = devm_platform_get_and_ioremap_resource(pdev, 0, &ioresource);
-	if (IS_ERR(p))
-		return PTR_ERR(p);
+	if (IS_ERR(p)) {
+		ret = PTR_ERR(p);
+		goto out_err;
+	}
 
 	pio->phys_addr = ioresource->start;
 
@@ -1359,6 +1366,7 @@ static int rp1_pio_probe(struct platform_device *pdev)
 	unregister_chrdev_region(pio->dev_num, 1);
 
 out_err:
+	g_pio = ERR_PTR(ret);
 	return ret;
 }