printk: Add match_devname_and_update_preferred_console()

Let's add match_devname_and_update_preferred_console() for driver
subsystems to call during init when the console is ready, and it's
character device name is known. For now, we use it only for the serial
layer to allow console=DEVNAME:0.0 style hardware based addressing for
consoles.

The earlier attempt on doing this caused a regression with the kernel
command line console order as it added calling __add_preferred_console()
again later on during init. A better approach was suggested by Petr where
we add the deferred console to the console_cmdline[] and update it later
on when the console is ready.

Suggested-by: Petr Mladek <pmladek@suse.com>
Co-developed-by: Petr Mladek <pmladek@suse.com>
Signed-off-by: Tony Lindgren <tony.lindgren@linux.intel.com>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20240703100615.118762-2-tony.lindgren@linux.intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

include/linux/printk.h

@@ -60,6 +60,10 @@ static inline const char *printk_skip_headers(const char *buffer)
 #define CONSOLE_LOGLEVEL_DEFAULT CONFIG_CONSOLE_LOGLEVEL_DEFAULT
 #define CONSOLE_LOGLEVEL_QUIET	 CONFIG_CONSOLE_LOGLEVEL_QUIET
 
+int match_devname_and_update_preferred_console(const char *match,
+					       const char *name,
+					       const short idx);
+
 extern int console_printk[];
 
 #define console_loglevel (console_printk[0])

kernel/printk/console_cmdline.h

@@ -6,6 +6,7 @@ struct console_cmdline
 {
 	char	name[16];			/* Name of the driver	    */
 	int	index;				/* Minor dev. to use	    */
+	char	devname[32];			/* DEVNAME:0.0 style device name */
 	bool	user_specified;			/* Specified by command line vs. platform */
 	char	*options;			/* Options for the driver   */
 #ifdef CONFIG_A11Y_BRAILLE_CONSOLE

kernel/printk/printk.c

@@ -2429,18 +2429,23 @@ static void set_user_specified(struct console_cmdline *c, bool user_specified)
 	console_set_on_cmdline = 1;
 }
 
-static int __add_preferred_console(const char *name, const short idx, char *options,
+static int __add_preferred_console(const char *name, const short idx,
+				   const char *devname, char *options,
 				   char *brl_options, bool user_specified)
 {
 	struct console_cmdline *c;
 	int i;
 
+	if (!name && !devname)
+		return -EINVAL;
+
 	/*
 	 * We use a signed short index for struct console for device drivers to
 	 * indicate a not yet assigned index or port. However, a negative index
-	 * value is not valid for preferred console.
+	 * value is not valid when the console name and index are defined on
+	 * the command line.
 	 */
-	if (idx < 0)
+	if (name && idx < 0)
 		return -EINVAL;
 
 	/*
@@ -2448,9 +2453,10 @@ static int __add_preferred_console(const char *name, const short idx, char *opti
 	 *	if we have a slot free.
 	 */
 	for (i = 0, c = console_cmdline;
-	     i < MAX_CMDLINECONSOLES && c->name[0];
+	     i < MAX_CMDLINECONSOLES && (c->name[0] || c->devname[0]);
 	     i++, c++) {
-		if (strcmp(c->name, name) == 0 && c->index == idx) {
+		if ((name && strcmp(c->name, name) == 0 && c->index == idx) ||
+		    (devname && strcmp(c->devname, devname) == 0)) {
 			if (!brl_options)
 				preferred_console = i;
 			set_user_specified(c, user_specified);
@@ -2461,7 +2467,10 @@ static int __add_preferred_console(const char *name, const short idx, char *opti
 		return -E2BIG;
 	if (!brl_options)
 		preferred_console = i;
-	strscpy(c->name, name, sizeof(c->name));
+	if (name)
+		strscpy(c->name, name);
+	if (devname)
+		strscpy(c->devname, devname);
 	c->options = options;
 	set_user_specified(c, user_specified);
 	braille_set_options(c, brl_options);
@@ -2486,8 +2495,13 @@ __setup("console_msg_format=", console_msg_format_setup);
  */
 static int __init console_setup(char *str)
 {
-	char buf[sizeof(console_cmdline[0].name) + 4]; /* 4 for "ttyS" */
-	char *s, *options, *brl_options = NULL;
+	static_assert(sizeof(console_cmdline[0].devname) >= sizeof(console_cmdline[0].name) + 4);
+	char buf[sizeof(console_cmdline[0].devname)];
+	char *brl_options = NULL;
+	char *ttyname = NULL;
+	char *devname = NULL;
+	char *options;
+	char *s;
 	int idx;
 
 	/*
@@ -2496,17 +2510,23 @@ static int __init console_setup(char *str)
 	 * for exactly this purpose.
 	 */
 	if (str[0] == 0 || strcmp(str, "null") == 0) {
-		__add_preferred_console("ttynull", 0, NULL, NULL, true);
+		__add_preferred_console("ttynull", 0, NULL, NULL, NULL, true);
 		return 1;
 	}
 
 	if (_braille_console_setup(&str, &brl_options))
 		return 1;
 
+	/* For a DEVNAME:0.0 style console the character device is unknown early */
+	if (strchr(str, ':'))
+		devname = buf;
+	else
+		ttyname = buf;
+
 	/*
 	 * Decode str into name, index, options.
 	 */
-	if (isdigit(str[0]))
+	if (ttyname && isdigit(str[0]))
 		scnprintf(buf, sizeof(buf), "ttyS%s", str);
 	else
 		strscpy(buf, str);
@@ -2523,12 +2543,18 @@ static int __init console_setup(char *str)
 #endif
 
 	for (s = buf; *s; s++)
-		if (isdigit(*s) || *s == ',')
+		if ((ttyname && isdigit(*s)) || *s == ',')
 			break;
-	idx = simple_strtoul(s, NULL, 10);
+
+	/* @idx will get defined when devname matches. */
+	if (devname)
+		idx = -1;
+	else
+		idx = simple_strtoul(s, NULL, 10);
+
 	*s = 0;
 
-	__add_preferred_console(buf, idx, options, brl_options, true);
+	__add_preferred_console(ttyname, idx, devname, options, brl_options, true);
 	return 1;
 }
 __setup("console=", console_setup);
@@ -2548,7 +2574,51 @@ __setup("console=", console_setup);
  */
 int add_preferred_console(const char *name, const short idx, char *options)
 {
-	return __add_preferred_console(name, idx, options, NULL, false);
+	return __add_preferred_console(name, idx, NULL, options, NULL, false);
+}
+
+/**
+ * match_devname_and_update_preferred_console - Update a preferred console
+ *	when matching devname is found.
+ * @devname: DEVNAME:0.0 style device name
+ * @name: Name of the corresponding console driver, e.g. "ttyS"
+ * @idx: Console index, e.g. port number.
+ *
+ * The function checks whether a device with the given @devname is
+ * preferred via the console=DEVNAME:0.0 command line option.
+ * It fills the missing console driver name and console index
+ * so that a later register_console() call could find (match)
+ * and enable this device.
+ *
+ * It might be used when a driver subsystem initializes particular
+ * devices with already known DEVNAME:0.0 style names. And it
+ * could predict which console driver name and index this device
+ * would later get associated with.
+ *
+ * Return: 0 on success, negative error code on failure.
+ */
+int match_devname_and_update_preferred_console(const char *devname,
+					       const char *name,
+					       const short idx)
+{
+	struct console_cmdline *c = console_cmdline;
+	int i;
+
+	if (!devname || !strlen(devname) || !name || !strlen(name) || idx < 0)
+		return -EINVAL;
+
+	for (i = 0; i < MAX_CMDLINECONSOLES && (c->name[0] || c->devname[0]);
+	     i++, c++) {
+		if (!strcmp(devname, c->devname)) {
+			pr_info("associate the preferred console \"%s\" with \"%s%d\"\n",
+				devname, name, idx);
+			strscpy(c->name, name);
+			c->index = idx;
+			return 0;
+		}
+	}
+
+	return -ENOENT;
 }
 
 bool console_suspend_enabled = true;
@@ -3318,8 +3388,11 @@ static int try_enable_preferred_console(struct console *newcon,
 	int i, err;
 
 	for (i = 0, c = console_cmdline;
-	     i < MAX_CMDLINECONSOLES && c->name[0];
+	     i < MAX_CMDLINECONSOLES && (c->name[0] || c->devname[0]);
 	     i++, c++) {
+		/* Console not yet initialized? */
+		if (!c->name[0])
+			continue;
 		if (c->user_specified != user_specified)
 			continue;
 		if (!newcon->match ||