driver: fall back to minimal functionality if an error occurs during probe

This patch add the capability to fall back to minimal functionality on error, to
allow reflashing cards with broken firmware.  It also fixes a kernel panic on
remove that previously occurred with unsupported cards.

Author: kashuwong

modules/exanic/exanic-main.c

@@ -951,7 +951,6 @@ static int exanic_probe(struct pci_dev *pdev,
     unsigned port_num;
     const char *hw_id_str;
     const char *function_str;
-    bool unsupported_exanic = false;
     uint32_t dma_cfg;
     u8 mac_addr[ETH_ALEN];
 
@@ -1051,44 +1050,21 @@ static int exanic_probe(struct pci_dev *pdev,
                 "Unsupported exanic interface version: %u (min %u, max %u)\n",
                 exanic->pcie_if_ver, MIN_SUPPORTED_PCIE_IF_VER,
                 MAX_SUPPORTED_PCIE_IF_VER);
-        unsupported_exanic = true;
+        goto err_interface_ver;
     }
 
     hw_id_str = exanic_hardware_id_str(exanic->hw_id);
     if (hw_id_str == NULL)
     {
         dev_err(dev, "Unsupported hardware type: %u\n", exanic->hw_id);
-        unsupported_exanic = true;
+        goto err_hw_id;
     }
 
     function_str = exanic_function_id_str(exanic->function_id);
     if (function_str == NULL)
     {
         dev_err(dev, "Unsupported function type: %u\n", exanic->function_id);
-        unsupported_exanic = true;
-    }
-
-    if (unsupported_exanic)
-    {
-        /* Minimal support for unsupported cards, to allow firmware update. */
-
-        /* Register device (misc_dev.minor already initialized) */
-        exanic->misc_dev.name = exanic->name;
-        exanic->misc_dev.fops = &exanic_fops;
-        exanic->unsupported = true;
-        exanic->num_ports = 0;
-        err = misc_register(&exanic->misc_dev);
-        if (err)
-        {
-            dev_err(dev, "misc_register failed: %d\n", err);
-            goto err_unsupported_exanic;
-        }
-
-        dev_info(dev, "Finished probing %s (minor = %u):\n",
-            exanic->name, exanic->misc_dev.minor);
-        dev_info(dev, "  Unknown exanic version, minimal support enabled\n");
-
-        return 0;
+        goto err_function_id;
     }
 
     /* Make sure card has completed its startup sequence */
@@ -1801,7 +1777,30 @@ static int exanic_probe(struct pci_dev *pdev,
         iounmap(exanic->tx_region_virt);
 err_dma_mask:
 err_timeout:
-err_unsupported_exanic:
+err_function_id:
+err_hw_id:
+err_interface_ver:
+
+    /* Minimal support for unsupported cards, to allow firmware update. */
+
+    /* Register device (misc_dev.minor already initialized) */
+    exanic->misc_dev.name = exanic->name;
+    exanic->misc_dev.fops = &exanic_fops;
+    exanic->unsupported = true;
+    exanic->num_ports = 0;
+    err = misc_register(&exanic->misc_dev);
+    if (!err)
+    {
+        dev_info(dev, "Finished probing %s (minor = %u):\n",
+            exanic->name, exanic->misc_dev.minor);
+        dev_info(dev, "  Error encountered during probe, minimal support enabled\n");
+        return 0;
+    }
+    else
+        dev_err(dev, "misc_register failed: %d\n", err);
+
+    /* If we get here, no device file was created and we need to error out */
+
     iounmap(exanic->regs_virt);
 err_regs_ioremap:
 err_regs_size:
@@ -1906,8 +1905,12 @@ static void exanic_remove(struct pci_dev *pdev)
     if (exanic->tx_region_virt != NULL)
         iounmap(exanic->tx_region_virt);
 
-    exanic_sysfs_exit(exanic);
-    exanic_i2c_exit(exanic);
+    if (!exanic->unsupported)
+    {
+        exanic_sysfs_exit(exanic);
+        exanic_i2c_exit(exanic);
+    }
+
     misc_deregister(&exanic->misc_dev);
 
     /* If a card reset has been requested post remove, trigger that just before