memory: tegra20-emc: Make driver modular

Add modularization support to the Tegra20 EMC driver, which now can be
compiled as a loadable kernel module.
Signed-off-by: Dmitry Osipenko <digetx@gmail.com>
Acked-by: Thierry Reding <treding@nvidia.com>
Link: https://lore.kernel.org/r/20201104164923.21238-34-digetx@gmail.comSigned-off-by: Krzysztof Kozlowski <krzk@kernel.org>

drivers/memory/tegra/Kconfig

@@ -9,7 +9,7 @@ config TEGRA_MC
 	  NVIDIA Tegra SoCs.
 
 config TEGRA20_EMC
-	bool "NVIDIA Tegra20 External Memory Controller driver"
+	tristate "NVIDIA Tegra20 External Memory Controller driver"
 	default y
 	depends on ARCH_TEGRA_2x_SOC
 	help

drivers/memory/tegra/tegra20-emc.c

@@ -721,6 +721,13 @@ static int tegra_emc_probe(struct platform_device *pdev)
 	platform_set_drvdata(pdev, emc);
 	tegra_emc_debugfs_init(emc);
 
+	/*
+	 * Don't allow the kernel module to be unloaded. Unloading adds some
+	 * extra complexity which doesn't really worth the effort in a case of
+	 * this driver.
+	 */
+	try_module_get(THIS_MODULE);
+
 	return 0;
 
 unset_cb:
@@ -733,6 +740,7 @@ static const struct of_device_id tegra_emc_of_match[] = {
 	{ .compatible = "nvidia,tegra20-emc", },
 	{},
 };
+MODULE_DEVICE_TABLE(of, tegra_emc_of_match);
 
 static struct platform_driver tegra_emc_driver = {
 	.probe = tegra_emc_probe,
@@ -742,9 +750,8 @@ static struct platform_driver tegra_emc_driver = {
 		.suppress_bind_attrs = true,
 	},
 };
+module_platform_driver(tegra_emc_driver);
 
-static int __init tegra_emc_init(void)
-{
-	return platform_driver_register(&tegra_emc_driver);
-}
-subsys_initcall(tegra_emc_init);
+MODULE_AUTHOR("Dmitry Osipenko <digetx@gmail.com>");
+MODULE_DESCRIPTION("NVIDIA Tegra20 EMC driver");
+MODULE_LICENSE("GPL v2");