[PATCH v2] serial: 8250: Keep 8250.<xxxx> module options functional after driver rename

[Josh Boyer <jwboyer@xxxxxxxxxx>]

With commit 835d844d1 (8250_pnp: do pnp probe before legacy probe), the
8250 driver was renamed to 8250_core.  This means any existing usage of
the 8259.<xxxx> module parameters or as a kernel command line switch is
now broken, as the 8250_core driver doesn't parse options belonging to
something called "8250".

To solve this, we redefine the module options in a dummy function using
a redefined MODULE_PARAM_PREFX when built into the kernel.  In the case
where we're building as a module, we provide an alias to the old 8250
name.  The dummy function prevents compiler errors due to global variable
redefinitions that happen as part of the module_param_ macro expansions.

Signed-off-by: Josh Boyer <jwboyer@xxxxxxxxxx>
---
 v2: Use __module_param_call for probe_rsa instead of undefining the
     __param_check macro as suggested by Jiri Slaby

 drivers/tty/serial/8250/8250.c | 29 +++++++++++++++++++++++++++++
 1 file changed, 29 insertions(+)

diff --git a/drivers/tty/serial/8250/8250.c b/drivers/tty/serial/8250/8250.c
index 0efc815..f982633 100644
--- a/drivers/tty/serial/8250/8250.c
+++ b/drivers/tty/serial/8250/8250.c
@@ -3396,3 +3396,32 @@ module_param_array(probe_rsa, ulong, &probe_rsa_count, 0444);
 MODULE_PARM_DESC(probe_rsa, "Probe I/O ports for RSA");
 #endif
 MODULE_ALIAS_CHARDEV_MAJOR(TTY_MAJOR);
+
+#ifndef MODULE
+/* This module was renamed to 8250_core in 3.7.  Keep the old "8250" name
+ * working as well for the module options so we don't break people.  We
+ * need to keep the names identical and the convenient macros will happily
+ * refuse to let us do that by failing the build with redefinition errors
+ * of global variables.  So we stick them inside a dummy function to avoid
+ * those conflicts.  The options still get parsed, and the redefined
+ * MODULE_PARAM_PREFIX lets us keep the "8250." syntax alive.
+ *
+ * This is hacky.  I'm sorry.
+ */
+static void __used s8250_options(void)
+{
+#undef MODULE_PARAM_PREFIX
+#define MODULE_PARAM_PREFIX "8250."
+
+	module_param_cb(share_irqs, &param_ops_uint, &share_irqs, 0644);
+	module_param_cb(nr_uarts, &param_ops_uint, &nr_uarts, 0644);
+	module_param_cb(skip_txen_test, &param_ops_uint, &skip_txen_test, 0644);
+#ifdef CONFIG_SERIAL_8250_RSA
+	__module_param_call(MODULE_PARAM_PREFIX, probe_rsa,
+		&param_array_ops, .arr = &__param_arr_probe_rsa,
+		0444, -1);
+#endif
+}
+#else
+MODULE_ALIAS("8250");
+#endif
-- 
1.8.1.2

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