[PATCH v3 1/3] printk: Save console options for add_preferred_console_match()

[Tony Lindgren]

Driver subsystems may need to translate the preferred console name to the
character device name used. We already do some of this in console_setup()
with a few hardcoded names, but that does not scale well.

The console options are parsed early in console_setup(), and the consoles
are added with __add_preferred_console(). At this point we don't know much
about the character device names and device drivers getting probed.

To allow drivers subsystems to set up a preferred console, let's save the
kernel command line console options. To add a preferred console, let's add
a new function add_preferred_console_match().

This allows the serial core layer to support console=DEVNAME:0.0 style
hardware based addressing in addition to the current console=ttyS0 style
naming. And we can start moving console_setup() character device parsing
to the driver subsystem specific code.

We use a separate array from the console_cmdline array as the character
device name and index may be unknown at the console_setup() time. And we do
not want to call __add_preferred_console() until the character device name
and index are known.

Adding the console name in addition to the character device name, and a
flag for an added console, could be added to the struct console_cmdline.
And the console_cmdline array handling modified accordingly. But that
complicates things compared saving the console options, and then adding
the consoles when the subsystems handling the consoles are ready.

Signed-off-by: Tony Lindgren <tony@xxxxxxxxxxx>
---
 include/linux/printk.h          |   3 +
 kernel/printk/Makefile          |   2 +-
 kernel/printk/conopt.c          | 115 ++++++++++++++++++++++++++++++++
 kernel/printk/console_cmdline.h |   4 ++
 kernel/printk/printk.c          |  11 ++-
 5 files changed, 131 insertions(+), 4 deletions(-)
 create mode 100644 kernel/printk/conopt.c

diff --git a/include/linux/printk.h b/include/linux/printk.h
--- a/include/linux/printk.h
+++ b/include/linux/printk.h
@@ -60,6 +60,9 @@ 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 add_preferred_console_match(const char *match, const char *name,
+				const short idx);
+
 extern int console_printk[];
 
 #define console_loglevel (console_printk[0])
diff --git a/kernel/printk/Makefile b/kernel/printk/Makefile
--- a/kernel/printk/Makefile
+++ b/kernel/printk/Makefile
@@ -1,5 +1,5 @@
 # SPDX-License-Identifier: GPL-2.0-only
-obj-y	= printk.o
+obj-y	= printk.o conopt.o
 obj-$(CONFIG_PRINTK)	+= printk_safe.o nbcon.o
 obj-$(CONFIG_A11Y_BRAILLE_CONSOLE)	+= braille.o
 obj-$(CONFIG_PRINTK_INDEX)	+= index.o
diff --git a/kernel/printk/conopt.c b/kernel/printk/conopt.c
new file mode 100644
--- /dev/null
+++ b/kernel/printk/conopt.c
@@ -0,0 +1,115 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Kernel command line console options for hardware based addressing
+ *
+ * Copyright (C) 2023 Texas Instruments Incorporated - https://www.ti.com/
+ * Author: Tony Lindgren <tony@xxxxxxxxxxx>
+ */
+
+#include <linux/console.h>
+#include <linux/kernel.h>
+
+#include "console_cmdline.h"
+
+/*
+ * Allow longer DEVNAME:0.0 style console naming such as abcd0000.serial:0.0
+ * in addition to the legacy ttyS0 style naming.
+ */
+#define CONSOLE_NAME_MAX	32
+
+#define CONSOLE_OPT_MAX		16
+
+struct console_option {
+	char name[CONSOLE_NAME_MAX];
+	char opt[CONSOLE_OPT_MAX];
+};
+
+/* Updated only at console_setup() time, no locking needed */
+static struct console_option conopt[MAX_CMDLINECONSOLES];
+
+/**
+ * console_opt_save - Saves kernel command line console option for driver use
+ * @str: Kernel command line console name and option
+ *
+ * Saves a kernel command line console option for driver subsystems to use for
+ * adding a preferred console during init. Called from console_setup() only.
+ */
+int __init console_opt_save(char *str)
+{
+	struct console_option *con;
+	const char *opt = NULL;
+	size_t namelen, optlen;
+	int i;
+
+	namelen = strcspn(str, ",");
+	if (!namelen)
+		return -EINVAL;
+
+	optlen = strlen(str) - namelen;
+	if (optlen > 1)
+		opt = str + namelen + 1;
+
+	if (namelen >= CONSOLE_NAME_MAX || optlen >= CONSOLE_OPT_MAX)
+		return -EINVAL;
+
+	for (i = 0; i < MAX_CMDLINECONSOLES; i++) {
+		con = &conopt[i];
+
+		if (con->name[0]) {
+			if (!strncmp(str, con->name, namelen))
+				return 0;
+			continue;
+		}
+
+		strscpy(con->name, str, namelen + 1);
+		if (opt)
+			strscpy(con->opt, opt, optlen + 1);
+
+		return 0;
+	}
+
+	return -ENOMEM;
+}
+
+static struct console_option *console_opt_find(const char *name)
+{
+	struct console_option *con;
+	int i;
+
+	for (i = 0; i < MAX_CMDLINECONSOLES; i++) {
+		con = &conopt[i];
+		if (!strcmp(name, con->name))
+			return con;
+	}
+
+	return NULL;
+}
+
+/**
+ * add_preferred_console_match - Adds a preferred console if a match is found
+ * @match: Expected console on kernel command line, such as console=DEVNAME:0.0
+ * @name: Name of the console character device to add such as ttyS
+ * @idx: Index for the console
+ *
+ * Allows driver subsystems to add a console after translating the command
+ * line name to the character device name used for the console. Options are
+ * added automatically based on the kernel command line. Duplicate preferred
+ * consoles are ignored by __add_preferred_console().
+ */
+int add_preferred_console_match(const char *match, const char *name,
+				const short idx)
+{
+	struct console_option *con;
+
+	if (!match || !strlen(match) || !name || !strlen(name) ||
+	    idx < 0)
+		return -EINVAL;
+
+	con = console_opt_find(match);
+	if (!con)
+		return -ENOENT;
+
+	add_preferred_console(name, idx, con->opt);
+
+	return 0;
+}
diff --git a/kernel/printk/console_cmdline.h b/kernel/printk/console_cmdline.h
--- a/kernel/printk/console_cmdline.h
+++ b/kernel/printk/console_cmdline.h
@@ -2,6 +2,10 @@
 #ifndef _CONSOLE_CMDLINE_H
 #define _CONSOLE_CMDLINE_H
 
+#define MAX_CMDLINECONSOLES 8
+
+int console_opt_save(char *str);
+
 struct console_cmdline
 {
 	char	name[16];			/* Name of the driver	    */
diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -360,9 +360,6 @@ static int console_locked;
 /*
  *	Array of consoles built from command line options (console=)
  */
-
-#define MAX_CMDLINECONSOLES 8
-
 static struct console_cmdline console_cmdline[MAX_CMDLINECONSOLES];
 
 static int preferred_console = -1;
@@ -2445,6 +2442,14 @@ static int __init console_setup(char *str)
 	char *s, *options, *brl_options = NULL;
 	int idx;
 
+	/*
+	 * Save the console for possible driver subsystem use. Bail out early
+	 * for DEVICE:0.0 style console names as the character device name is
+	 * be unknown at this point.
+	 */
+	if (!console_opt_save(str) && strchr(str, ':'))
+		return 1;
+
 	/*
 	 * console="" or console=null have been suggested as a way to
 	 * disable console output. Use ttynull that has been created
-- 
2.42.1